Napster branded an "utter failure" by record industry

The Recording Industry Association of America (RIAA) has also called on the courts to enforce their earlier ruling against Shawn Fanning's controversial music swapping site - which so far seems to have been flouted by the high school drop out and his legion of music lovers.

Raising the pitch of the ongoing legal battle, the RIAA made its comments in papers submitted to a US district court.

It said Napster's filtering system was "archaic", and called on it to adopt an "opt-in" system, where only specifically authorised music is able to be shared.

The RIAA is trying to shut the file-sharing service down - claiming the sharing of files infringes artists' copyright. Last month US judge Marilyn Patel issued an injunction ordering Napster to prevent access to all files of copyrighted music. However, this decision also laid the onus on the record companies to provide the names of the files that should be blocked.

Napster users have tried to get around the blocking of files by re-naming them with slight variations in spelling which Napster's filtering software struggles to detect.

In response to yesterday's filing, Napster said the RIAA was dodging its responsibilities by not helping to identify copyrighted music, adding it had already blocked access to over half the files on its service.