The trade group representing the U.S. music industry has filed a new round of lawsuits against 744 people it alleges used online file-sharing networks to illegally trade in copyrighted songs, it said on Wednesday. The Recording Industry Association of America said the various suits, filed in courts across the country, cover "John Doe" defendants whose true identities are unknown to the group.

Separately, suits covering 152 people who were previously sued anonymously but later identified and offered the chance to settle, were refiled with their true identities after they ignored or declined those offers, an RIAA spokesman said.

The RIAA said the individuals it sued used a variety of Internet platforms to swap songs, including Limewire, Grokster, Kazaa and eDonkey.

Including the 744 from Wednesday, the RIAA has sued nearly 4,700 people since last September in its efforts to combat piracy, which the music industry has blamed for a multiyear decline in CD sales. Some music fans have countered that bad music, and not piracy, was to blame for the decline.

Last week a federal appeals court held that makers of file-sharing software could not be held liable for certain kinds of copyright infringement, dealing a blow to efforts by the movie and music industries to stop at the source the exchange of files they say has cost them billions.

The RIAA represents the world's largest record labels, such as Warner Music, EMI Group Plc (EMI.L) and the music arms of Bertelsmann AG (BERT.UL), Sony Corp. (6758.T) and Vivendi Universal (NYSE:V - news).