Agena (computer virus)
Encyclopedia
AGENA is a memory resident, file infecting computer virus
which infects .COM
and .EXE
files, including command.com
. It was discovered in Spain in September, 1992. Upon infection, Agena becomes memory resident at the top of system memory but below the 640K DOS
boundary. Once it is memory resident, Agena infects .COM and .EXE files as they are executed. Infected programs will have a file length increase of 723 to 738 byte
s with the virus being located at the end of the file. An infected file's date and time in the DOS disk directory listing are not altered. Total system and available free memory, as indicated by the DOS CHKDSK program, will have decreased by 1,296 bytes. Interrupt
s 20 and 21 are hooked by the virus. It is unknown what Agena may do besides replicate. No text strings are visible within the viral code in infected programs.
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...
which infects .COM
COM file
In many computer operating systems, a COM file is a type of executable file; the name is derived from the file name extension .COM. Originally, the term stood for "Command file", a text file containing commands to be issued to the operating system , on many of the Digital Equipment Corporation mini...
and .EXE
EXE
EXE is the common filename extension denoting an executable file in the DOS, OpenVMS, Microsoft Windows, Symbian, and OS/2 operating systems....
files, including command.com
COMMAND.COM
COMMAND.COM is the filename of the default operating system shell for DOS operating systems and the default command line interpreter on Windows 95, Windows 98 and Windows Me...
. It was discovered in Spain in September, 1992. Upon infection, Agena becomes memory resident at the top of system memory but below the 640K DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
boundary. Once it is memory resident, Agena infects .COM and .EXE files as they are executed. Infected programs will have a file length increase of 723 to 738 byte
Byte
The byte is a unit of digital information in computing and telecommunications that most commonly consists of eight bits. Historically, a byte was the number of bits used to encode a single character of text in a computer and for this reason it is the basic addressable element in many computer...
s with the virus being located at the end of the file. An infected file's date and time in the DOS disk directory listing are not altered. Total system and available free memory, as indicated by the DOS CHKDSK program, will have decreased by 1,296 bytes. Interrupt
Interrupt
In computing, an interrupt is an asynchronous signal indicating the need for attention or a synchronous event in software indicating the need for a change in execution....
s 20 and 21 are hooked by the virus. It is unknown what Agena may do besides replicate. No text strings are visible within the viral code in infected programs.
External links
- Computer Viruses (A), by Probert Encyclopedia
- Agena virus, by McAfee