The popular music-sharing Internet service Napster received a heavy blow to its struggle to stay alive yesterday, as a court ruling indicated the service is likely to be shut down pending a final ruling on the matter.

The pre-trial injunction requiring Napster to shut down--issued last July by the District Court of Northern California and then stayed by the Ninth Circuit Court of Appeals in August--was effectively sent back to the district court yesterday for modification.

Although Napster remains accessible for the moment, when the district court rewords its decision the service will be unavailable--only reopening if Napster should emerge victorious from its final trial.

The three-judge appeals court panel that delivered yesterday's ruling explained that the original injunction expected too much of Napster.

The opinion stated that although it is Napster's responsibility to police its system to the best of its ability, the burden is on the plaintiffs to notify Napsters of copyrighted works on its system.

The panel also advised the district court to take into account the difficulties facing Napster in gaining access to users' MP3 files, given the fact that most files are user-named.

However, the panel made it very clear that Napster users infringe on copyrights, and that "Napster materially contributes to the infringing activity."

In a statement released yesterday, Napster CEO Hank Barry acknowledged that the service could be shut down before trial.