Aimster lets its users swap any files stored on their computers with other Aimster users. MP3 music files are the most popular transfers among its users. The system is similar to Napster’s MP3 swapping service, however, unlike Napster, transfers on Aimster are encrypted - making it difficult for copyright owners to know what files are being swapped by users.
The RIAA sent a warning letter to Aimster, saying that its service is close enough to Napster’s for it to violate the same copyright laws. Aimster refused to comply with the RIAA's demands to block the transfer of copyrighted material and instead, tried pre-empting the legal action. Last month, Aimster sought a declaration from its local court in Albany, New York, that its service is legal. Its argument is that anyone wanting to show copyright infringement would themselves have to break the law by breaking into personal networks.
Rather than await the judge’s decision on Aimster’s claim, the RIAA has sued in New York City on behalf of all major and some independent record labels. General Counsel for the RIAA said: “Aimster is Napster all over again.” According to reports, a similar lawsuit is expected from the movie industry.