Antivirus software
Encyclopedia
Antivirus or anti-virus software is used to prevent, detect, and remove malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...

, including but not limited to computer virus
Computer virus
A computer virus is a computer program that can replicate itself and spread from one computer to another. The term "virus" is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware programs that do not have the reproductive ability...

es, computer worm
Computer worm
A computer worm is a self-replicating malware computer program, which uses a computer network to send copies of itself to other nodes and it may do so without any user intervention. This is due to security shortcomings on the target computer. Unlike a computer virus, it does not need to attach...

, trojan horses
Trojan horse (computing)
A Trojan horse, or Trojan, is software that appears to perform a desirable function for the user prior to run or install, but steals information or harms the system. The term is derived from the Trojan Horse story in Greek mythology.-Malware:A destructive program that masquerades as a benign...

, spyware
Spyware
Spyware is a type of malware that can be installed on computers, and which collects small pieces of information about users without their knowledge. The presence of spyware is typically hidden from the user, and can be difficult to detect. Typically, spyware is secretly installed on the user's...

 and adware
Adware
Adware, or advertising-supported software, is any software package which automatically plays, displays, or downloads advertisements to a computer. These advertisements can be in the form of a pop-up. They may also be in the user interface of the software or on a screen presented to the user during...

. This page talks about the software used for the prevention and removal of such threats
Threat (computer)
In Computer security a threat is a possible danger that might exploit a vulnerability to breach security and thus cause possible harm.A threat can be either "intentional" or "accidental" In Computer security a threat is a possible danger that might exploit a vulnerability to breach security and...

, rather than computer security
Computer security
Computer security is a branch of computer technology known as information security as applied to computers and networks. The objective of computer security includes protection of information and property from theft, corruption, or natural disaster, while allowing the information and property to...

 implemented by software methods.

A variety of strategies are typically employed. Signature-based detection involves searching for known patterns of data within executable code. However, it is possible for a computer to be infected with new malware for which no signature is yet known. To counter
Countermeasure (computer)
In Computer Security a countermeasure is an action, device, procedure, or technique that reduces a threat, a vulnerability, or an attack by eliminating or preventing it, by minimizing the harm it can cause, or by discovering and reporting it so that corrective action can be taken.The definition is...

 such so-called zero-day threats, heuristics can be used. One type of heuristic approach, generic signatures, can identify new viruses or variants of existing viruses by looking for known malicious code, or slight variations of such code, in files. Some antivirus software can also predict what a file will do by running it in a sandbox
Sandbox (computer security)
In computer security, a sandbox is a security mechanism for separating running programs. It is often used to execute untested code, or untrusted programs from unverified third-parties, suppliers, untrusted users and untrusted websites....

 and analyzing what it does to see if it performs any malicious actions.

No matter how useful antivirus software can be, it can sometimes have drawbacks. Antivirus software can impair a computer's performance
Computer performance
Computer performance is characterized by the amount of useful work accomplished by a computer system compared to the time and resources used.Depending on the context, good computer performance may involve one or more of the following:...

. Inexperienced users may also have trouble understanding the prompts and decisions that antivirus software presents them with. An incorrect decision may lead to a security breach. If the antivirus software employs heuristic detection, success depends on achieving the right balance between false positives and false negatives. False positives can be as destructive as false negatives. Finally, antivirus software generally runs at the highly trusted kernel
Kernel (computing)
In computing, the kernel is the main component of most computer operating systems; it is a bridge between applications and the actual data processing done at the hardware level. The kernel's responsibilities include managing the system's resources...

 level of the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

, creating a potential avenue of attack
Attack (computer)
In computer and computer networks an attack is any attempt to destroy, expose, alter, disable, steal or gain unauthorized access to or make unauthorized use of an asset.- IETF :Internet Engineering Task Force defines attack in RFC 2828 as:...

.

History

Most of the computer viruses written in the early and mid 1980s were limited to self-reproduction and had no specific damage routine built into the code. That changed when more and more programmers became acquainted with virus programming and created viruses that manipulated or even destroyed data on infected computers.

There are competing claims for the innovator of the first antivirus product. Possibly the first publicly documented removal of a computer virus in the wild was performed by Bernd Fix
Bernd Fix
Bernd Fix is a German Hacker and Computer Security Expert.- Biography :After final secondary-school examination from Gymnasium Hankensbüttel in 1981, Bernd Fix studied Astrophysics and Philosophy at the universities of Göttingen and Heidelberg...

 in 1987. There were also two antivirus applications for the Atari ST
Atari ST
The Atari ST is a home/personal computer that was released by Atari Corporation in 1985 and commercially available from that summer into the early 1990s. The "ST" officially stands for "Sixteen/Thirty-two", which referred to the Motorola 68000's 16-bit external bus and 32-bit internals...

 platform developed in 1987. The first one was G Data
G Data
G Data Software is a collection of anti-malware solutions by G Data Software, Inc. It was founded in Bochum, Germany in 1985 with the North American subsidiary currently located in Durham, North Carolina, U. S. A. G Data is able to achieve higher detection rates than other products...

  and second was UVK 2000.

Fred Cohen
Fred Cohen
Frederick B. Cohen is an American computer scientist and best known as the inventor of computer virus defense techniques.In 1983, while a student at the University of Southern California's School of Engineering , he wrote a program for a parasitic application that seized control of computer...

, who published one of the first academic papers on computer viruses in 1984, began to develop strategies for antivirus software in 1988 that were picked up and continued by later antivirus software developers.

Also in 1988 a mailing list named VIRUS-L was started on the BITNET
BITNET
BITNET was a cooperative USA university network founded in 1981 by Ira Fuchs at the City University of New York and Greydon Freeman at Yale University...

/EARN network where new viruses and the possibilities of detecting and eliminating viruses were discussed. Some members of this mailing list like John McAfee
John McAfee
John McAfee is a computer programmer and founder of McAfee. He was one of the first people to design anti-virus software and to develop a virus scanner. He was born in England and raised in Salem, Virginia...

 or Eugene Kaspersky
Eugene Kaspersky
Eugene Kaspersky is a specialist in the information security field. He has written articles on computer virology and speaks regularly at security seminars and conferences...

 later founded software companies that developed and sold commercial antivirus software.

Before internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

 connectivity was widespread, viruses were typically spread by infected floppy disk
Floppy disk
A floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...

s. Antivirus software came into use, but was updated relatively infrequently. During this time, virus checkers essentially had to check executable files and the boot sectors of floppy disks and hard disks. However, as internet usage became common, viruses began to spread online.

Over the years it has become necessary for antivirus software to check an increasing variety of files, rather than just executables, for several reasons:
  • Powerful macros used in word processor
    Word processor
    A word processor is a computer application used for the production of any sort of printable material....

     applications, such as Microsoft Word
    Microsoft Word
    Microsoft Word is a word processor designed by Microsoft. It was first released in 1983 under the name Multi-Tool Word for Xenix systems. Subsequent versions were later written for several other platforms including IBM PCs running DOS , the Apple Macintosh , the AT&T Unix PC , Atari ST , SCO UNIX,...

    , presented a risk. Virus writers could use the macros to write viruses embedded within documents. This meant that computers could now also be at risk from infection by opening documents with hidden attached macros.
  • The possibility of embedding executable objects inside otherwise non-executable file formats can make opening those files a risk.
  • Later email programs, in particular Microsoft's Outlook Express
    Outlook Express
    Outlook Express is an email and news client that is included with Internet Explorer versions 4.0 through 6.0. As such, it is also bundled with several versions of Microsoft Windows, from Windows 98 to Windows Server 2003, and is available for Windows 3.x, Windows NT 3.51, Windows 95 and Mac OS 9...

     and Outlook
    Microsoft Outlook
    Microsoft Outlook is a personal information manager from Microsoft, available both as a separate application as well as a part of the Microsoft Office suite...

    , were vulnerable
    Vulnerability (computing)
    In computer security, a vulnerability is a weakness which allows an attacker to reduce a system's information assurance.Vulnerability is the intersection of three elements: a system susceptibility or flaw, attacker access to the flaw, and attacker capability to exploit the flaw...

     to viruses embedded in the email body itself. A user's computer could be infected by just opening or previewing a message.


As always-on broadband connections became the norm, and more and more viruses were released, it became essential to update virus checkers more and more frequently. Even then, a new zero-day virus could become widespread before antivirus companies released an update to protect against it.

Identification methods

There are several methods which antivirus software can use to identify malware.

Signature based detection is the most common method. To identify viruses and other malware, antivirus software compares the contents of a file to a dictionary
Associative array
In computer science, an associative array is an abstract data type composed of a collection of pairs, such that each possible key appears at most once in the collection....

 of virus signatures. Because viruses can embed themselves in existing files, the entire file is searched, not just as a whole, but also in pieces.

Heuristic
Heuristic
Heuristic refers to experience-based techniques for problem solving, learning, and discovery. Heuristic methods are used to speed up the process of finding a satisfactory solution, where an exhaustive search is impractical...

-based detection
, like malicious activity detection, can be used to identify unknown viruses.

File emulation is another heuristic approach. File emulation involves executing a program in a virtual environment
Virtual machine
A virtual machine is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or both together.-VM Definitions:A virtual machine is a software...

 and logging what actions the program performs. Depending on the actions logged, the antivirus software can determine if the program is malicious or not and then carry out the appropriate disinfection actions.

Signature-based detection

Traditionally, antivirus software heavily relied upon signatures to identify malware. This can be very effective, but cannot defend against malware unless samples have already been obtained and signatures created. Because of this, signature-based approaches are not effective against new, unknown viruses.

As new viruses are being created each day, the signature-based detection approach requires frequent updates of the virus signature dictionary. To assist the antivirus software companies, the software may allow the user to upload new viruses or variants to the company, allowing the virus to be analyzed and the signature added to the dictionary.

Although the signature-based approach can effectively contain virus outbreaks, virus authors have tried to stay a step ahead of such software by writing "oligomorphic
Oligomorphic code
An oligomorphic engine is generally used by a computer virus to generate a decryptor for itself in a way comparable to a simple polymorphic engine. It does this by randomly selecting each piece of the decryptor from several predefined alternatives....

", "polymorphic
Polymorphic code
In computer terminology, polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact. That is, the code changes itself each time it runs, but the function of the code will not change at all...

" and, more recently, "metamorphic
Metamorphic code
In computer virus terms, metamorphic code is code that can reprogram itself. Often, it does this by translating its own code into a temporary representation, editing the temporary representation of itself, and then writing itself back to normal code again. This procedure is done with the virus...

" viruses, which encrypt parts of themselves or otherwise modify themselves as a method of disguise, so as to not match virus signatures in the dictionary.

Heuristics

Some more sophisticated antivirus software uses heuristic analysis to identify new malware or variants of known malware.

Many viruses start as a single infection and through either mutation
Mutation (genetic algorithm)
In genetic algorithms of computing, mutation is a genetic operator used to maintain genetic diversity from one generation of a population of algorithm chromosomes to the next...

 or refinements by other attackers, can grow into dozens of slightly different strains, called variants. Generic detection refers to the detection and removal of multiple threats using a single virus definition.

For example, the Vundo trojan
Trojan horse (computing)
A Trojan horse, or Trojan, is software that appears to perform a desirable function for the user prior to run or install, but steals information or harms the system. The term is derived from the Trojan Horse story in Greek mythology.-Malware:A destructive program that masquerades as a benign...

 has several family members, depending on the antivirus vendor's classification. Symantec
Symantec
Symantec Corporation is the largest maker of security software for computers. The company is headquartered in Mountain View, California, and is a Fortune 500 company and a member of the S&P 500 stock market index.-History:...

 classifies members of the Vundo family into two distinct categories, Trojan.Vundo and Trojan.Vundo.B.

While it may be advantageous to identify a specific virus, it can be quicker to detect a virus family through a generic signature or through an inexact match to an existing signature. Virus researchers find common areas that all viruses in a family share uniquely and can thus create a single generic signature. These signatures often contain non-contiguous code, using wildcard character
Wildcard character
-Telecommunication:In telecommunications, a wildcard character is a character that may be substituted for any of a defined subset of all possible characters....

s where differences lie. These wildcards allow the scanner to detect viruses even if they are padded with extra, meaningless code. A detection that uses this method is said to be "heuristic detection."

Rootkit detection

Anti-virus software can attempt to scan for rootkits; a rootkit
Rootkit
A rootkit is software that enables continued privileged access to a computer while actively hiding its presence from administrators by subverting standard operating system functionality or other applications...

 is a type of malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...

 that is designed to gain administrative-level control over a computer system without being detected. Rootkits can change how the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 functions and in some cases can tamper with the anti-virus program and render it ineffective. Rootkits are also difficult to remove, in some cases requiring a complete re-installation of the operating system.

Unexpected renewal costs

Some commercial antivirus software end-user license agreements include a clause that the subscription will be automatically renewed, and the purchaser's credit card automatically billed, at the renewal time without explicit approval. For example, McAfee
McAfee
McAfee, Inc. is a computer security company headquartered in Santa Clara, California, USA. It markets software and services to home users, businesses and the public sector. On August 19, 2010, electronics company Intel agreed to purchase McAfee for $7.68 billion...

 requires users to unsubscribe at least 60 days before the expiration of the present subscription while BitDefender
BitDefender
BitDefender is an antivirus software suite developed by Romania-based software company Softwin. It was launched in November 2001, and is currently in its 15 build version...

 sends notifications to unsubscribe 30 days before the renewal. Norton Antivirus
Norton AntiVirus
Norton AntiVirus, developed and distributed by Symantec Corporation, provides malware prevention and removal during a subscription period. It uses signatures and heuristics to identify viruses. Other features include e-mail spam filtering and phishing protection.Symantec distributes the product as...

 also renews subscriptions automatically by default.

Rogue security applications

Some apparent antivirus programs are actually malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...

 masquerading as legitimate software, such as WinFixer
WinFixer
WinFixerAlso known under various other names including: WinAntiVirusPro, ErrorSafe, SystemDoctor, WinAntiSpyware, AVSystemCare, WinAntiSpy, Windows Police Pro, Performance Optimizer, StorageProtector, PrivacyProtector, WinReanimator, DriveCleaner, WinspywareProtect, PCTurboPro, FreePCSecure,...

, MS Antivirus, and Mac Defender
Mac Defender
Mac Defender is an internet rogue security program that can be installed by unwitting users of computers running the Mac OS X operating system. The Mac security firm Intego discovered the fake antivirus software on May 2, 2011, with a patch not being provided by Apple until May 31...

.

Problems caused by false positives

A "false positive" is when antivirus software identifies a non-malicious file as a virus. When this happens, it can cause serious problems. For example, if an antivirus program is configured to immediately delete or quarantine infected files, a false positive in an essential file can render the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 or some applications unusable. In May 2007, a faulty virus signature issued by Symantec
Symantec
Symantec Corporation is the largest maker of security software for computers. The company is headquartered in Mountain View, California, and is a Fortune 500 company and a member of the S&P 500 stock market index.-History:...

 mistakenly removed essential operating system files, leaving thousands of PCs unable to boot
Boot
A boot is a type of footwear but they are not shoes. Most boots mainly cover the foot and the ankle and extend up the leg, sometimes as far as the knee or even the hip. Most boots have a heel that is clearly distinguishable from the rest of the sole, even if the two are made of one piece....

. Also in May 2007, the executable file
Executable
In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...

 required by Pegasus Mail
Pegasus Mail
Pegasus Mail is a donationware , proprietary, email client that is developed and maintained by David Harris and his team. It was originally released in 1990 for internal and external mail on Netware networks with MS-DOS clients, and was subsequently ported to Microsoft Windows...

 was falsely detected by Norton AntiVirus
Norton AntiVirus
Norton AntiVirus, developed and distributed by Symantec Corporation, provides malware prevention and removal during a subscription period. It uses signatures and heuristics to identify viruses. Other features include e-mail spam filtering and phishing protection.Symantec distributes the product as...

 as being a Trojan and it was automatically removed, preventing Pegasus Mail from running. Norton anti-virus had falsely identified three releases of Pegasus Mail as malware, and would delete the Pegasus Mail installer file when that happened. In response to this Pegasus Mail stated:
In April 2010, McAfee VirusScan
McAfee VirusScan
McAfee VirusScan is an antivirus program created and maintained by McAfee Inc. . McAfee markets VirusScan to home and home-office users; McAfee also develops VirusScan Enterprise for use in corporate environments...

 detected svchost.exe, a normal Windows binary, as a virus on machines running Windows XP with Service Pack 3, causing a reboot loop and loss of all network access.

In December 2010, a faulty update on the AVG anti-virus suite damaged 64-bit versions of Windows 7, rendering it unable to boot, due to an endless boot loop created.

In October 2011, Microsoft Security Essentials removed the Google Chrome
Google Chrome
Google Chrome is a web browser developed by Google that uses the WebKit layout engine. It was first released as a beta version for Microsoft Windows on September 2, 2008, and the public stable release was on December 11, 2008. The name is derived from the graphical user interface frame, or...

 browser, rival to Microsoft's own Internet Explorer
Internet Explorer
Windows Internet Explorer is a series of graphical web browsers developed by Microsoft and included as part of the Microsoft Windows line of operating systems, starting in 1995. It was first released as part of the add-on package Plus! for Windows 95 that year...

. MSE flagged Chrome as a Zbot banking trojan
Zeus (trojan horse)
Zeus is a Trojan horse that steals banking information by keystroke logging and Form Grabbing. Zeus is spread mainly through drive-by downloads and phishing schemes. First identified in July 2007 when it was used to steal information from the United States Department of Transportation, it became...

.

When Microsoft Windows becomes damaged by faulty anti-virus products, fixing the damage to Microsoft Windows incurs technical support costs and businesses can be forced to close whilst remedial action is undertaken.

System and interoperability related issues

Running multiple antivirus programs concurrently can degrade performance and create conflicts. However, using a concept called multiscanning
Multiscanning
Multiscanning is running multiple anti-malware or antivirus engines concurrently. Traditionally, only a single engine can actively scan a system at a given time. Using multiple engines simultaneously can result in conflicts that lead to system freezes and application failures...

, several companies (including G Data
G Data
G Data Software is a collection of anti-malware solutions by G Data Software, Inc. It was founded in Bochum, Germany in 1985 with the North American subsidiary currently located in Durham, North Carolina, U. S. A. G Data is able to achieve higher detection rates than other products...

 and Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...

) have created applications which can run multiple engines concurrently.

It is sometimes necessary to temporarily disable virus protection when installing major updates such as Windows Service Packs or updating graphics card drivers. Active antivirus protection may partially or completely prevent the installation of a major update.

A minority of software programs are not compatible with anti-virus software. For example, the TrueCrypt
TrueCrypt
TrueCrypt is a software application used for on-the-fly encryption . It is free and open source. It can create a virtual encrypted disk within a file or encrypt a partition or the entire storage device .- Operating systems :TrueCrypt supports Microsoft Windows, Mac OS X, and...

 troubleshooting page reports that anti-virus programs can conflict with TrueCrypt and cause it to malfunction.

Support issues also exist around antivirus application interoperability with common solutions like SSL VPN remote access and network access control
Network Access Control
Network Access Control is an approach to computer network security that attempts to unify endpoint security technology , user or system authentication and network security enforcement.-Background:Network Access Control is a computer networking solution that uses a set of protocols to define and...

 products. These technology solutions often have policy assessment applications which require that an up to date antivirus is installed and running. If the antivirus application is not recognized by the policy assessment, whether because the antivirus application has been updated or because it is not part of the policy assessment library, the user will be unable to connect.

Effectiveness

Studies in December 2007 showed that the effectiveness of antivirus software had decreased in the previous year, particularly against unknown or zero day attacks. The computer magazine c't
C't
c't – Magazin für Computertechnik is a German computer magazine, published by the Heinz Heise publishing house. Originally a special section of the electronics magazine elrad, the magazine has been published monthly since December 1983 and biweekly since October 1997...

found that detection rates for these threats had dropped from 40-50% in 2006 to 20-30% in 2007. At that time, the only exception was the NOD32
NOD32
ESET NOD32 Antivirus, commonly known as NOD32, is an antivirus software package made by the Slovak company ESET. ESET NOD32 Antivirus is sold in two editions, Home Edition and Business Edition...

 antivirus, which managed a detection rate of 68 percent.

The problem is magnified by the changing intent of virus authors. Some years ago it was obvious when a virus infection was present. The viruses of the day, written by amateurs, exhibited destructive behavior or pop-up
Pop-up ad
Pop-up ads or pop-ups are a form of online advertising on the World Wide Web intended to attract web traffic or capture email addresses. Pop-ups are generally new web browser windows to display advertisements...

s. Modern viruses are often written by professionals, financed by criminal organization
Organized crime
Organized crime or criminal organizations are transnational, national, or local groupings of highly centralized enterprises run by criminals for the purpose of engaging in illegal activity, most commonly for monetary profit. Some criminal organizations, such as terrorist organizations, are...

s.

Independent testing on all the major virus scanners consistently shows that none provide 100% virus detection. The best ones provided as high as 99.6% detection, while the lowest provided only 81.8% in tests conducted in February 2010. All virus scanners produce false positive results as well, identifying benign files as malware.

Although methodologies may differ, some notable independent quality testing agencies include AV-Comparatives, ICSA Labs, West Coast Labs, VB100
Virus Bulletin
Virus Bulletin is a magazine about the prevention, detection and removal of malware and spam. It regularly features analyses of the latest virus threats, articles exploring new developments in the fight against viruses, interviews with anti-virus experts, and evaluations of current anti-malware...

 and other members of the Anti-Malware Testing Standards Organization.

New viruses

Anti-virus programs are not always effective against new viruses, even those that use non-signature-based methods that should detect new viruses. The reason for this is that the virus designers test their new viruses on the major anti-virus applications to make sure that they are not detected before releasing them into the wild.

Some new viruses, particularly ransomware
Ransomware (malware)
Ransomware is computer malware which holds a computer system, or the data it contains, hostage against its user by demanding a ransom for its restoration.- Operation :...

, use polymorphic code
Polymorphic code
In computer terminology, polymorphic code is code that uses a polymorphic engine to mutate while keeping the original algorithm intact. That is, the code changes itself each time it runs, but the function of the code will not change at all...

 to avoid detection by virus scanners. Jerome Segura, a security analyst with ParetoLogic, explained:
A proof of concept
Proof of concept
A proof of concept or a proof of principle is a realization of a certain method or idea to demonstrate its feasibility, or a demonstration in principle, whose purpose is to verify that some concept or theory that has the potential of being used...

 virus has used the Graphics Processing Unit
Graphics processing unit
A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...

 (GPU) to avoid detection from anti-virus software. The potential success of this involves bypassing the CPU
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 in order to make it much harder for security researchers to analyse the inner workings of such malware.

Rootkits

Detecting rootkit
Rootkit
A rootkit is software that enables continued privileged access to a computer while actively hiding its presence from administrators by subverting standard operating system functionality or other applications...

s is a major challenge for anti-virus programs. Rootkits have full administrative access to the computer and are invisible to users and hidden from the list of running processes in the task manager
Task manager
A task manager is a program used to provide information about the processes and programs running on a computer, as well as the general status of the computer. It can also be used to terminate processes and programs, as well as change the processes priority...

. Rootkits can modify the inner workings of the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

 and tamper with antivirus programs.

Damaged files

Files which have been damaged by computer viruses are normally damaged beyond recovery. Anti-virus software removes the virus code from the file during disinfection, but this does not always restore the file to its undamaged state. In such circumstances, damaged files can only be restored from existing backups; installed software that is damaged requires re-installation.

Firmware issues

Active anti-virus software can interfere with a firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...

 update process. Any writeable firmware in the computer can be infected by malicious code. This is a major concern, as an infected BIOS
BIOS
In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....

 could require the actual BIOS chip to be replaced to ensure the malicious code is completely removed. Anti-virus software is not effective at protecting firmware and the motherboard
Motherboard
In personal computers, a motherboard is the central printed circuit board in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals. The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple...

 BIOS from infection.

Other methods

Installed antivirus software running on an individual computer is only one method of guarding against viruses. Other methods are also used, including cloud-based antivirus, firewalls and on-line scanners.

Cloud antivirus

Cloud antivirus is a technology that uses lightweight agent software on the protected computer, while offloading the majority of data analysis to the provider's infrastructure.

One approach to implementing cloud antivirus involves scanning suspicious files using multiple antivirus engines. This approach was proposed by an early implementation of the cloud antivirus concept called CloudAV. CloudAV was designed to send programs or documents to a network cloud
Cloud computing
Cloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network ....

 where multiple antivirus and behavioral detection programs are used simultaneously in order to improve detection rates. Parallel scanning of files using potentially incompatible antivirus scanners is achieved by spawning a virtual machine per detection engine and therefore eliminating any possible issues. CloudAV can also perform "retrospective detection," whereby the cloud detection engine rescans all files in its file access history when a new threat is identified thus improving new threat detection speed. Finally, CloudAV is a solution for effective virus scanning on devices that lack the computing power to perform the scans themselves.

Network firewall

Network firewalls
Firewall (computing)
A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....

 prevent unknown programs and processes from accessing the system. However, they are not antivirus systems and make no attempt to identify or remove anything. They may protect against infection from outside the protected computer or network
Län
Län and lääni refer to the administrative divisions used in Sweden and previously in Finland. The provinces of Finland were abolished on January 1, 2010....

, and limit the activity of any malicious software which is present by blocking incoming or outgoing requests on certain TCP/IP ports. A firewall is designed to deal with broader system threats that come from network connections into the system and is not an alternative to a virus protection system.

Online scanning

Some antivirus vendors maintain websites with free online scanning capability of the entire computer, critical areas only, local disks, folders or files. Periodic online scanning is a good idea for those that run antivirus applications on their computers because those applications are frequently slow to catch threats. One of the first things that malicious software does in an attack is disable any existing antivirus software and sometimes the only way to know of an attack is by turning to an online resource that isn't already installed on the infected computer.

Specialist tools

Virus removal tools are available to help remove stubborn infections or certain types of infection. Examples include Trend Micro
Trend Micro
Trend Micro Inc. is a computer security company. It is headquartered in Tokyo, Japan and markets Trend Micro Internet Security, Trend Micro Worry-Free Business Security, OfficeScan, and other related security products and services...

's Rootkit Buster, and rkhunter
Rkhunter
rkhunter is a Unix-based tool that scans for rootkits, backdoors and possible local exploits. It does this by comparing SHA-1 hashes of important files with known good ones in online database, searching for default directories , wrong permissions, hidden files, suspicious strings in kernel...

 for the detection of rootkit
Rootkit
A rootkit is software that enables continued privileged access to a computer while actively hiding its presence from administrators by subverting standard operating system functionality or other applications...

s, Avira
Avira
Avira Operations GmbH & Co. KG is a German antivirus software company. When founded, the company was called "H+BEDV Datentechnik GmbH". Its antivirus applications are based on the AntiVir scan engine also known as "Luke Filewalker" , first launched in 1988. For aesthetic reasons, the name was...

's AntiVir Removal Tool, PCTools
PC Tools (company)
PC Tools , formerly known as WinGuides.com, is a software company headquartered in Australia with offices in the USA, UK, Ireland and Ukraine. It develops and distributes security and optimization software for the Mac OS X and Microsoft Windows platforms. There are over 200 employees...

 Threat Removal Tool
, and AVG's Anti-Virus Free 2011.

A rescue disk that is bootable, such as a CD or USB storage device, can be used to run antivirus software outside of the installed operating system, in order to remove infections while they are dormant. A bootable antivirus disk can be useful when, for example, the installed operating system is no longer bootable or has malware that is resisting all attempts to be removed by the installed antivirus software. Examples of some of these bootable disks include the Avira
Avira
Avira Operations GmbH & Co. KG is a German antivirus software company. When founded, the company was called "H+BEDV Datentechnik GmbH". Its antivirus applications are based on the AntiVir scan engine also known as "Luke Filewalker" , first launched in 1988. For aesthetic reasons, the name was...

 AntiVir Rescue System
, PCTools
PC Tools (company)
PC Tools , formerly known as WinGuides.com, is a software company headquartered in Australia with offices in the USA, UK, Ireland and Ukraine. It develops and distributes security and optimization software for the Mac OS X and Microsoft Windows platforms. There are over 200 employees...

 Alternate Operating System Scanner
, and AVG Rescue CD. The AVG Rescue CD software can also be installed onto a USB storage device, that is bootable on newer computers.

Popularity

According to an FBI survey, major businesses lose $12 million annually dealing with virus incidents. A survey by Symantec
Symantec
Symantec Corporation is the largest maker of security software for computers. The company is headquartered in Mountain View, California, and is a Fortune 500 company and a member of the S&P 500 stock market index.-History:...

 in 2009 found that a third of small to medium sized business did not use antivirus protection at that time, whereas more than 80% of home users had some kind of antivirus installed.

See also

  • EICAR
    EICAR
    EICAR, the European Institute for Computer Antivirus Research, was founded in 1991 as an organization aiming to further antivirus research and improving development of antivirus software...

    , the European Institute for Computer Antivirus Research
  • Linux malware
    Linux malware
    Linux malware includes viruses, trojans, worms and other types of malware that affect the Linux operating system. Linux, Unix and other Unix-like computer operating systems are generally regarded as very well-protected, but not immune, from computer viruses...

  • List of antivirus software
  • List of computer viruses
  • List of trojan horses
  • Quarantine technology
    Quarantine technology
    Quarantine Technology is a function of virus protection software that voluntarily isolates any infected files on a computers hard disk. Quarantine Technology protects these infected files from corrupting other files on a computer....

  • Sandbox (computer security)
    Sandbox (computer security)
    In computer security, a sandbox is a security mechanism for separating running programs. It is often used to execute untested code, or untrusted programs from unverified third-parties, suppliers, untrusted users and untrusted websites....

  • Timeline of notable computer viruses and worms
    Timeline of notable computer viruses and worms
    This is a timeline of noteworthy computer viruses, worms and Trojan horses.- 1966 :* The work of John von Neumann on the "Theory of self-reproducing automata" is published...

  • Virus hoax
    Virus hoax
    A computer virus hoax is a message warning the recipient of a non-existent computer virus threat. The message is usually a chain e-mail that tells the recipient to forward it to everyone they know.-Identification:...

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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