The new software, called Morpheus Preview Edition, is based on open-source Gnutella technology, software that has been a mainstay of the file-swapping world since 2000. Until Tuesday's surprise shutdown, the Morpheus service was based on technology licensed from Dutch company Kazaa BV.

"We are pleased to migrate to an open protocol product with the release of Morpheus Preview Edition, which is based on the very large network of Gnutella users," company Chief Executive Steve Griffin said in a statement.

The release of the Gnutella-based Morpheus could dramatically change the balance of power in the file-swapping world.

Morpheus users had previously formed the largest group of a three-part file-swapping network, which included members using Kazaa Media Desktop and Grokster software. All three services used technology licensed from Kazaa BV. The services formed a pool of member computers from which anyone could search for songs or other files.

According to CNET Download.com, a software aggregation site operated by News.com publisher CNET Networks, Morpheus had been downloaded more than 51 million times. The Kazaa Media Desktop, which is now owned by Australian company Sharman Networks, had been downloaded more than 37 million times.

On Tuesday, Morpheus users found themselves locked out of the network and were alerted by the software that an upgrade was needed to reconnect. Although Sharman Networks and Grokster were distributing a new version of the file-swapping software, StreamCast's Griffin said his service had not been offered the upgrade. In recent days, he has dubbed the shutdown of his software an "attack" against Morpheus users, although he hasn't said who was responsible for the attack.

Griffin said Friday that his company has had some dispute over terms and fees with software creator Kazaa BV. He said throwing his users off the network would violate terms of his contract with Kazaa BV, however.

Executives of Kazaa BV could not be reached for comment.

The new version of Morpheus will search computers on the Gnutella network, which includes computers running software such as LimeWire or BearShare, but will not connect to computers running Kazaa Media Desktop or Grokster.

If a significant fraction of Morpheus' old user base decides to use the new software, it will represent a considerable step forward for the 2-year-old Gnutella. Use of the open-source software has always trailed far behind that of Napster, Morpheus or Kazaa.

Sharman Networks, meanwhile, has been taking advantage of Morpheus' initial shutdown to lure the giant's users. Since Wednesday the service has had a note on its Web site that reads, "Morpheus users, come on over to our place." On Friday, it also released a new piece of software that helped convert Morpheus users to the Kazaa software.

"Kazaa Media DeskTop gives (computer users) all Morpheus did, and much more," Nicola Hemming, Sharman's CEO, said in a statement. "Our focus has always been on optimizing the user's experience."

StreamCast, Grokster and Kazaa BV are being sued by the big record labels and Hollywood studios over copyright concerns in Los Angeles federal court. A hearing in that case is scheduled for March 4. Sharman Networks, which purchased the Kazaa Media Desktop from Dutch Kazaa BV, has not been sued.