What Is Leecher?

Downloading, and usually uploading at the same time

A leecher is a peer in a BitTorrent swarm that does not yet have the complete file. It is downloading pieces from other peers and, in nearly all cases, it is also uploading the pieces it already holds. BitTorrent is designed that way: as soon as a client has verified a piece, it offers that piece to the rest of the swarm. A peer that finishes the download and keeps sharing becomes a seeder.

Where the word comes from

In file-sharing communities, "leecher" began as an insult for someone who takes without giving back, for example by closing the client the moment a download completes or throttling upload to almost nothing. Private trackers enforce share ratios precisely to discourage this. In client software and on index sites, though, the word is neutral and simply means a peer that is still downloading. The neutral sense is the one that matters for analysis.

Leecher, downloader and infringer are three different claims

It is tempting to read a leecher count as a number of infringers. That skips several steps. A peer in a swarm may be a monitoring tool, a researcher, a misconfigured client, or a user who picked up a fake file under a popular name. Even where the content is genuine, whether the activity infringes depends on the rights position and on the law of the country concerned, and countries treat downloading and making available in different ways.

There is also a technical distinction worth holding on to. Because a leecher normally uploads while it downloads, it is usually also making pieces available to others. In many legal systems, making a work available is the act that enforcement concentrates on, more than the download itself.

Why leechers still matter in evidence

For a rights holder, leechers are mainly a signal of demand. A swarm with many leechers and few seeders shows strong interest in a title and a supply that depends on a small number of sources. That is exactly when acting on those sources, and on the index pages recruiting new peers, has the most effect.

Where leechers are recorded as evidence, the record should show that pieces of the protected work were actually received from that peer and verified against the known hash, with address, port and timestamp. Appearing in a peer list is not enough on its own: lists can include stale entries, and some contain addresses that were never part of the transfer at all.