A group of motion picture and recording companies filed a copyright infringement suit Wednesday against a network of firms offering Internet users free downloads of pirated music and movies.

The group of around 30 plaintiffs includes Sony Music Entertainment Inc., Columbia Pictures Industries Inc., Time Warner Entertainment Co., Twentieth Century Fox Film Corp. and Disney Enterprises Inc. They filed the lawsuit with the federal district court in Los Angeles against MusicCity Networks Inc. (www.musiccity.com) and other developers and distributors of the free services.

The defendants had "developed and control a network largely dedicated to the repeated and exploitative unauthorized distribution and reproduction of plaintiff's protected works," the suit said.

"We cannot sit idly by while these services continue to operate illegally, especially at a time when new legitimate services are being launched," Hilary Rosen, president of the Recording Industry Association of America, said in a statement.

The defendants have developed a technology that allows users to find and trade files with each other directly, avoiding the centralized server-based system that Napster had used.

Earlier this year, a U.S. court ordered Napster to cease maintaining a network of users that were engaged in trading copyrighted music.