From the Wikipedia:
"An anonymous P2P computer network is a particular type of peer-to-peer network in which the users are anonymous or pseudonymous by default. The primary difference between regular and anonymous networks is in the routing method of their respective network architectures. These networks allow the unfettered free flow of information.
Interest in anonymous P2P has increased in recent years for many reasons, including distrust of governments, mass surveillance and data retention, and lawsuits against bloggers. Such networks may also appeal to those wishing to share potentially copyrighted files - organizations such as the Recording Industry Association of America and the British Phonographic Industry have successfully tracked and sued users on non-anonymous P2P networks." (http://en.wikipedia.org/wiki/Anonymous_P2P)