Metallica famously filed a lawsuit against Napster in 2000 over copyright infringement, becoming one of the most high-profile cases in the digital music piracy era. The lawsuit specifically targeted Napster's peer-to-peer file-sharing service which allowed users to exchange MP3 files freely. The other options (LimeWire, Azureus, Kazaa) were also P2P networks but Metallica's legal action was specifically against Napster.