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In computing and specifically in Internet slang, a leech 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. The term originated in the bulletin board system era, when it referred to users that would download files and upload nothing in return.

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 word is also used without any pejorative connotations,[1][2] simply meaning to download large sets of information: for example the offline reader Leech, the Usenet newsreader NewsLeecher, the audio recording software SoundLeech, or LeechPOP, a utility to download attachments from POP3 mailboxes.

The name derives from the leech, an animal that sucks blood and then tries to leave unnoticed. Other terms are used, such as "freeloader", "mooch" and "sponge", but leech is the most commonly used.



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In games (whether a traditional tabletop RPG, LARPing, or even MMORPG) 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", who is avoiding confrontation.


P2P networks

Amongst users of the BitTorrent file distribution protocol and common P2P networks, such as the eDonkey network or Gnutella2, a leech is a user who disconnects as soon as they have 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 do not have the complete file yet). As BitTorrent clients 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 they 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 they have finished downloading and continue to run the client. They 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. 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 of the amount of data a client uploads or downloads to avoid leeching, while on real P2P networks systems like DLP (Dynamic Leecher Protection) (eMule Xtreme Mod, eDonkey network) or uploader rewarding (Gnutella2) have been brought in place. Note that BitTorrent is not a P2P network, it is only a P2P file distribution system.

Leeching is often seen as a threat to peer-to-peer sharing and as the direct opposite of the practice of seeding. But with rising downloads, uploads are still guaranteed, although few contributors in the system account for most services.[3]

See also


  1. ^ Wang, Wally (2004). Steal this File Sharing Book: What They Won't Tell You about File Sharing. No Starch Press. ISBN 978-1-59327-050-6. Retrieved 6 June 2020. Leech sites [...] provide free, unlimited access to all the files you want.
  2. ^ Narins, Brigham (2002). World of Computer Science. Gale Group. p. 6. ISBN 978-0-7876-5067-4. Retrieved 6 June 2020. leech mode is the jargon terminology for an access mode on an FTP site that allows the user to download any number of files
  3. ^ Yang, S., Jin, H., Liao, X., Yao, H., Huang, Q., Tu, X. (2009). Measuring Web Feature Impacts In Peer-To-Peer File Sharing Systems. Hushing University of Science and Technology