A US district court has ordered a preliminary injunction against online file-swapping service Madster.

The company has now become the target of the legal might of music industry lawyers fresh from their victory against Napster.

More than two dozen record and other media companies are involved in the litigation, which they claim violates copyright law in a similar way to Napster.

Chief Judge Marvin Aspen, of the Chicago District Court, said that he made the order because Madster's "very raison d'être appears to be the facilitation of ... copyright infringement on a massive scale".

He gave the companies suing Madster, formerly known as Aimster, until next week to propose language for a "narrowly tailored" injunction that would end the copyright infringement.

He added that the injunction should allow room for "non-infringing uses of the Aimster system, if any, to continue".

Madster founder Johnny Deep told news agency Reuters that he didn't think there was a lot of copyrighted material on the system.

The Recording Industry Association of America admitted that it didn't know how many files shared on Madster are copyrighted, although an official said that it was probably at the same levels as Napster, at around 87 per cent.

Madster provides a $4.95 a month subscription service that offers file recommendations made by other members.