Napster users over the weekend may have found themselves unable to trade music, as the service began blocking access to thousands of copyrighted songs.
After a court hearing in San Francisco on Friday, no legal ruling was issued, but Napster said it would voluntarily start blocking access to songs on a list provided by record companies, individual artists and publishers.
The expected ruling will clarify to what extent Napster must ferret out copyrighted files traded on its network or merely respond to notices from the copyright owners.
The case highlights concern by portals and Internet service providers that they may have to devote significant resources to policing their networks for copyright infringement.
A section of the 1998 Digital Millennium Copyright Act (DMCA) says that service providers, broadly defined, cannot be held liable for infringements by their users, as long as they respond to official notices from copyright owners informing them of specific infringements.
A recent ruling by an appeals court, companies said, undermines that protection and could have serious economic consequences.
The Feb. 6 ruling by the U.S. Court of Appeals for the 4th Circuit held that RemarQ Communities, an ISP recently acquired by Critical Path, was liable for contributory copyright infringement because it hosts two Usenet newsgroups that contain hundreds of copyrighted "adult" photographs.
That decision, which overturned a lower courts ruling, said that since the newsgroups primarily contained photos copyrighted by the plaintiff, ALS Scan, a notice citing the two newsgroups and giving a partial list of copyrighted photos was sufficient notification.