Peer to Peer (P2P) file sharing uses individual client computers rather than central servers to host files and to make those files available to other users over the Internet. While not inherently illegal, P2P technologies are frequently used to download and share copyrighted materials, such as movies and music. Bittorrent, Gnuttela, Kazaa, and Limewire are examples of P2P programs that may be used to exchange files of copyrighted materials.
Using a P2P program to share files of copyrighted materials is a violation of the US Copyright Law. If you engage in the sharing of copyrighted materials, you may be subject to both criminal and civil action. If you are found to have infringed on copyright, you may be liable for damages up to $30,000 for each infringement. If willful infringement is proven, damages can be as high as $150,000
Educause provides a list of sites that can be used for legal downloading of movies, music, and other copyrighted works.