Thus the search request propagates across Gnutella space. A variation on Gnutella is Aimster, which uses America Online's messaging service to do the matchmaking between users who wish to exchange files, and then uses Gnutella to perform the actual transfers. From a legal point of view, Aimster is particularly cunning because it has all the advantages of Gnutella yet is designed for use by small groups of people who already communicate via instant messaging. He has created a system in which information can be posted and retrieved anonymously, and in such a way that it cannot be censored or modified. One problem that these file-distribution systems have is that not all users are prepared to muck in.
Many users download files from others without making their own files available in return.
A study by the Xerox Palo Alto Research Center in California, which looked at the behaviour of Gnutella users, found that 70 per cent of them offered no files to download. Just 20 per cent of Gnutella's users provided 98 per cent of the files in the system, and the most generous 1 per cent provided 40 per cent of the total. This opens the way to real-world payments for downloads, by establishing a link between Mojo and real money. But such arguments are unlikely to cut much ice with the RIAA or Hollywood. The music industry has been slow to embrace the internet.