The Motion Picture Association of America (MPAA) also made available a new free software tool so parents can scan their computers for file-swapping programs and for movie or music files which may be copyrighted.
The group said its lawsuits were targeting people across the United States, but did not say how many people were being sued.
"We cannot allow people to steal our motion pictures and other products online, and we will use all the options we have available to encourage people to obey the law," MPAA Chief Executive Officer Dan Glickman said in a statement. "We had to resort to lawsuits as one option to help make that happen."
After initially letting record labels take the lead, movie studios have launched their own aggressive legal campaigns against online film-trading in recent months, targeting individual computer users as well as Web site and server operators that serve as hubs of file-trading networks.
The group filed its first set of lawsuits against individual computer users in November, and followed up with a worldwide campaign against the operators of BitTorrent, eDonkey and DirectConnect networks.
As a result, some of the most popular Web sites that served as file-trading hubs, such as Suprnova.org and Yourceff.com. At least one, LokiTorrent.com, has remained online and is soliciting donations from its visitors to pay for legal fees.
The MPAA's new software, "Parent File Scan," is aimed at identifying file-swapping software applications and multimedia files on a computer, so that--in theory--parents can evaluate whether the files on their computer have been legally acquired and talk with children about the legalities of peer-to-peer activity. Unlike the network-monitoring software often installed in businesses or corporate networks, the MPAA-backed software does not monitor or block downloads.
In practice, the software, developed by the DtecNet Software company in Denmark, casts an extremely wide net.
It searches for and identifies virtually any audio or video file, including popular formats like MP3, Microsoft's Windows Media, the AAC files that Apple Computer's iTunes software often uses, or MPEG video. The software makes no distinction between legally acquired or illegally downloaded files, however--which can total in the thousands.
Parent File Scan also uses a very liberal definition of file-swapping software. In a test on a CNET News.com computer, the software identified Mirc--a client for the Internet Relay Chat network, where files can be swapped, but where tens of thousands of wholly legal conversations happen every day--and Mercora, a streaming Web radio service thatbut does not allow file swapping.
The software is primarily aimed at use by parents, and does not report any information back to the MPAA or any other group, the trade association said.