Block these ranges in your firewall:
18.104.22.168 - 22.214.171.124
126.96.36.199 - 188.8.131.52
184.108.40.206 - 220.127.116.11
then go here to see why:
[UPDATE] these guys are working for Wind-Up Records...a small label that is an RIAA member. When I was able to browse a few of the ones sharing files (not the annoying ones that get in your queue, but others of same usernames that you find on song searches) all the files they were "sharing" had one label in common, Wind-Up.