Leech (computing)
In computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...

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

, a leech or leecher is one who benefits, usually deliberately, from others' information or effort but does not offer anything in return, or makes only token offerings in an attempt to avoid being called a leech. In economics this type of behavior is called "free riding" and is associated with the free rider problem
Free rider problem
In economics, collective bargaining, psychology, and political science, a free rider is someone who consumes a resource without paying for it, or pays less than the full cost. The free rider problem is the question of how to limit free riding...


Depending on context, leeching does not necessarily refer to illegal use of computer resources, but often instead to greedy use according to etiquette: to wit, using too much of what is freely given without contributing a reasonable amount back to the community that provides it.

The name derives from the leech
Leeches are segmented worms that belong to the phylum Annelida and comprise the subclass Hirudinea. Like other oligochaetes such as earthworms, leeches share a clitellum and are hermaphrodites. Nevertheless, they differ from other oligochaetes in significant ways...

, an animal that sucks blood and then tries to leave unnoticed. Other terms are used, such as "freeloader", but leech is the most common.


  • Wi-Fi
    Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...

     leeches attach to open wireless networks without the owner's knowledge in order to access the Internet. One example of this is someone who connects to a café's free wireless service from his or her car in the parking lot in order to download large amounts of data.
  • Direct linking is a form of bandwidth leeching that occurs when placing an unauthorized linked object, often an image, from one site in a web page belonging to a second site (the leech).
  • In most P2P
    Peer-to-peer file sharing
    P2P or Peer-to-peer file sharing allows users to download files such as music, movies, and games using a P2P software client that searches for other connected computers. The "peers" are computer systems connected to each other through internet. Thus, the only requirements for a computer to join...

    -networks, leeching can be defined as behavior consisting of downloading more data, over time, than the individual is uploading to other clients, thus draining speed from the network. The term is used in a similar way for shared FTP directories. Mainly, leeching is taking without giving.
  • Claiming credit for, or offering for sale, freely available content created and uploaded by others to the Internet (Plagiarism
    Plagiarism is defined in dictionaries as the "wrongful appropriation," "close imitation," or "purloining and publication" of another author's "language, thoughts, ideas, or expressions," and the representation of them as one's own original work, but the notion remains problematic with nebulous...

    Copyfraud is a term used by Jason Mazzone, an Associate Professor of Law at Brooklyn Law School, to describe the use of false claims of copyright to attempt to control works not under one's legal control.-Introduction:Mazzone describes copyfraud as:...



In games (whether a traditional tabletop RPG, LARPing
Live action role-playing game
A live action role-playing game is a form of role-playing game where the participants physically act out their characters' actions. The players pursue goals within a fictional setting represented by the real world, while interacting with each other in character. The outcome of player actions may...

, or even MMORPG
Massively multiplayer online role-playing game is a genre of role-playing video games in which a very large number of players interact with one another within a virtual game world....

) the term "leech" is given to someone who avoids confrontation and sits out while another player fights and gains experience for the person, or "leecher(S)", who is avoiding confrontation.
  • In online multi-player games, "to leech" generally means that a player be present and qualify for the presentation of a reward of some sort, without contributing to the team effort needed to earn that reward. Although in the past the term "leeching" has been applied to a player gaining any benefit due solely to the efforts of others, the term is now most often limited to players that gain experience
    Experience point
    An experience point is a unit of measurement used in many role-playing games and role-playing video games to quantify a player character's progression through the game...

     without meaningful contribution. However, while this usually carries negative connotations, this is not always the case; for instance, in MMO's where Power Leveling is possible, a higher level player may deliberately consent to a lower leveled player gaining experience without assisting, usually due to the danger to the lower leveled player. In situations where the amount of assistance the lower level player can provide is negligible (as is often the case when being Power Leveled, due to the disparity between target mobs and the player), a higher level player may deliberately encourage the lower level player to "leech" to avoid wasted time spent protecting the lower level player that could otherwise be directed towards more quickly accomplishing the goal of earning experience points. However, this is usually an arrangement between friends or guild-mates, and unsolicited requests to "leech" experience off of a higher level player is often considered extremely rude.
  • In popular MMORPG's the alternative way to refer to a "leecher" (especially one that is "leeching" items, as opposed to experience) has arisen as being "Ninja" (referring to the notional lightning reflexes needed to claim the reward between its appearance and its retrieval by the more deserving player). This can be used as either a noun ("Player One is a loot ninja!") or a verb ("Player One keeps ninja'ing all the drops!"). However, a "ninja" may not necessarily be "leeching", in that they do sometimes contribute to the goal, "ninja" more applies towards a player claiming an item unfairly, either because the group agreed to pass the item to a particular player in advance, or by taking the item before the group can determine which player gets the item fairly through whichever process the group agreed upon (usually rolling for it, which is simulated in many MMOs through a "/random" or "/roll" command).
  • This is different from "killstealing" where a player uses an attack at the right moment to kill an enemy and take the experience benefit (XP), which may benefit the player or not. In some games, XP is granted to the person who deals a final shot to an enemy, or to who deals a significant amount of damage regardless of who hit it last. Killstealing can in this fashion be applied as a reverse leeching: it prevents another player from gaining XP at all regardless of their effort.


  • Wi-Fi networks can implement various authentication and access control technologies in order to prevent leeching. The most common are client MAC address
    MAC address
    A Media Access Control address is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies, including Ethernet...

     authorization tables (deprecated due to insecurity), Wired Equivalent Privacy
    Wired Equivalent Privacy
    Wired Equivalent Privacy is a weak security algorithm for IEEE 802.11 wireless networks. Introduced as part of the original 802.11 standard ratified in September 1999, its intention was to provide data confidentiality comparable to that of a traditional wired network...

     (deprecated due to insecurity), and Wi-Fi Protected Access
    Wi-Fi Protected Access
    Wi-Fi Protected Access and Wi-Fi Protected Access II are two security protocols and security certification programs developed by the Wi-Fi Alliance to secure wireless computer networks...

  • Bandwidth leeching can be prevented by running an anti-leeching script on the website's server. It can automatically ban IPs that leech, or can redirect them to faulty files.

P2P networks and BitTorrent

Among users of the BitTorrent file distribution
File sharing
File sharing is the practice of distributing or providing access to digitally stored information, such as computer programs, multimedia , documents, or electronic books. It may be implemented through a variety of ways...

 protocol and common P2P networks, such as the eDonkey network
EDonkey network
The eDonkey network is a decentralized, mostly server-based, peer-to-peer file sharing network best suited to share big files among users, and to provide long term availability of files...

 or Gnutella2
Gnutella2, often referred to as G2, is a peer-to-peer protocol developed mainly by Michael Stokes and released in 2002. While inspired by the gnutella protocol, G2 shares little of its design with the exception of its connection handshake and download mechanics. It adopts an extensible binary...

, a leech is a user who disconnects as soon as he/she has a complete copy of a particular file, while minimizing or completely suppressing data upload.

However, on most BitTorrent tracker sites, the term leecher is used for all users who are not seeders (which means they don't have the complete file yet). As BitTorrent clients
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....

 usually begin to upload files almost as soon as they have started to download them, such users are usually not freeloaders (people who don't upload data at all to the swarm). Therefore this kind of leeching is considered to be a legitimate practice. Reaching an upload/download ratio of 1:1 (meaning that the user has uploaded as much as he/she has downloaded) in a BitTorrent client is considered a minimum in the etiquette of that network. In the terminology of these BitTorrent sites, a leech becomes a seeder (a provider of the file) when he or she finished downloading and continues to run the client. He will remain a seeder until the file is removed or destroyed (settings enable the torrent to stop seeding at a certain share ratio, or after X hours have passed seeding).

The so-called bad leechers are those running specially modified clients which avoid uploading data. These clients are quite common because the tendency to open source
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 has made it relatively easy for modders to change the source code of most file sharing clients accordingly. This has led to the development of a multitude of technologies to ban such misbehaving clients. For example, on BitTorrent, most private trackers do keep track on the amount of data a client uploads or downloads to avoid leeching, while on other P2P networks it is only a P2P file distribution system - systems like DLP (Dynamic Leecher Protection) (eMule Xtreme Mod
Xtreme Mod
eMule Xtreme Mod is a free peer-to-peer file sharing application for Microsoft Windows based on eMule, released under the GNU General Public License, coded in Microsoft Visual C++. It connects to the eDonkey network and the Kad network...

, eDonkey network
EDonkey network
The eDonkey network is a decentralized, mostly server-based, peer-to-peer file sharing network best suited to share big files among users, and to provide long term availability of files...

) or uploader rewarding (Gnutella2
Gnutella2, often referred to as G2, is a peer-to-peer protocol developed mainly by Michael Stokes and released in 2002. While inspired by the gnutella protocol, G2 shares little of its design with the exception of its connection handshake and download mechanics. It adopts an extensible binary...

) have been brought in place.
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