Not anonymous attack reveals BitTorrent users on Tor network

An ingenious attack by French researchers has found a way to identify BitTorrent users even when they attempt to obscure their connections by using the Tor onion-routing network�and the researchers have already deployed it against 10,000 users.

Source:
http://arstechnica.com/tech-policy/news/2011/04/not-anonymous-attack-reveals-bittorrent-users-on-tor-network.ars