(09-24) 07:27 PDT LOS ANGELES (AP) --

Makers of the most popular online file-sharing network are suing entertainment companies for copyright infringement, alleging the companies used unauthorized versions of its software to snoop on users in their efforts to battle piracy.

Sharman Networks, the company behind the Kazaa file-sharing software, filed a federal lawsuit Monday, accusing the movie studios and the Recording Industry of America of using "Kazaa Lite," a replica of its software without advertising, to get onto the network. Sharman claims its copyright was violated because Kazaa Lite is an unauthorized version of its free software.

Once on the network, the companies offered bogus versions of copyright music and movies and then sent online messages to users warning them they were breaking the law. Sharman claims those moves violated terms for using its network.

The RIAA, which has battled the widespread sharing of music, called Sharman's "newfound admiration for the importance of copyright law" ironic and "self-serving."

Sharman's lawsuit also revives its previous allegation that Universal Music Group and Warner Music Group violated antitrust laws by stopping Sharman and its partner Altnet Inc. from distributing authorized copies of music and movies through Kazaa.

Last year the companies filed suit against Sharman, accusing it of providing free access to copyright music and films to millions of Internet users in the United States.

Sharman, in a countersuit, claimed movie and recording industries didn't understand the digital age and were monopolizing entertainment.

U.S. District Judge Stephen V. Wilson rejected those claims in July but last week allowed Sharman to try again.

Universal Music Group and Warner Music Group declined to comment on Sharman's latest lawsuit.

Users can download Kazaa file-sharing software, which hooks them up to a network where they can copy songs and movies without having to pay for them.

Earlier this month, recording companies sued 261 music fans, claiming they were illegally distributing hundreds of digital song files apiece over the Internet. The industry trolled file-sharing networks such as Kazaa and downloaded song files from users' computers.