1. n. (Also leecher.) Among BBS types, crackers and warez d00dz, one who consumes knowledge without generating new software, cracks, or techniques. BBS culture specifically defines a leech as someone who downloads files with few or no uploads in return, and who does not contribute to the message section. Cracker culture extends this definition to someone (a lamer, usually) who constantly presses informed sources for information and/or assistance, but has nothing to contribute. See troughie.
2. v. [common, Toronto area] v. To download a file across any kind of internet link. “Hop on IRC later so I can leech some MP3s from you.” Used to describe activities ranging from FTP, to IRC DCC-send, to ICQ file requests, to Napster searches (but never to downloading email with file attachments; the implication is that the download is the result of a browse or search of some sort of file server). Seems to be a holdover from the early 1990s when Toronto had a very active BBS and warez scene. Synonymous with snarf (sense 2), and contrast snarf (sense 4).