Altnet is a company created by Brilliant Digital Entertainment and Joltid. Joltid is the company KaZaA's founders' formed after they sold KaZaA to Sharman Networks. The lawsuit targets the RIAA, two anti-piracy companies Overpeer, Inc., Loudeye Corp., and individuals at these companies.
Basically, the filing states that the RIAA and two anti-piracy organizations have developed their own technology to access the P2P networks and track pirated media file usage. Because they are doing this programmatically, they have replicated the patented software developed by Altnet and in so doing violated their patent.
Altnet apparently has sent many warnings to the RIAA and its cohorts last November, but did not have an affect. InternetDJ will be watching this story closely.