Content owners and their associations (in the U.S., the RIAA and MPAA) are developing more sophisticated techniques for detecting pirated content. Two articles: The first from a pro-sharing site focused on the Bit Torrent technology discussing methods in the U.K. ; the second an article on software employed by copyright holders to track and identify infringers.

http://torrentfreak.com/this-is-how-we-catch-you-downloading/
http://www.fortwayne.com/mld/journalgazette/business/17072317.htm