I just read a post on Pirate Bay (an index site for Torrents and also a tracker) which says that the MediaDefender company, an anti-"piracy" company, in cooperation with major entertainment companies have been trying to harm trackers and other P2P networks even by using users' computers. This information was obtained from some leaked emails of the company that were published by the MediaDefender-Defenders group along with a phone call between MediaDefender and New York Attorney General's office.
MediaDefender denies everything and took legal action to remove the leaked emails from the sites that host them. But legal actions were not enough for them so they even performed DoS attacks to the site that hosted the leaked emails. MediaDefender had also previously vandalized the Wikipedia article about itself, probably because it revealed the connection of the company with miivi.com, a site that trapped people who uploaded copyrighted content.
You can visit this site and read the emails (which have been edited so that the identity of the employees cannot be revealed). Even in the case of the site going down you can still find the emails and the phone call in Torrents. Just search on The Pirate Bay for "MediaDefender".
For more information read the Wikipedia article on MediaDefender and this article.