The movie industry is training its legal guns on the Gnutella file-sharing system in its latest efforts to combat piracy. The Motion Picture Association of America (MPAA ) has sent hundreds of letters to major Internet service providers and universities, warning them that some people on their networks are violating the Digital Millennium Copyright Act (DMCA) by trading copyrighted movies through Gnutella. DMCA is similar to new copyright rules that were recently adopted by the European Commission. No action is believed to have been taken against European institutions or companies. Some of the universities that have been targeted in the MPAA's investigation include Harvard University and the University of Connecticut. Meanwhile, ISP Excite@Home has sent out about 20 e-mails and letters over the past four days telling Gnutella users their services will be terminated within 24 hours if their alleged movie sharing continues. "What we're trying to do is educate the population about what is appropriate, both from an ethical standpoint and from a legal standpoint," said Ken Jacobson, MPAA senior vice president of worldwide anti-piracy. The MPAA already has aggressively -- and successfully -- sued several companies, accusing them of aiding copyright infringement by allowing people to record and trade copyrighted content. They include Scour, iCraveTV.com and RecordTV.com. But until now, Gnutella systems have flown below the legal radar screen of many copyright holders, partly because it's so difficult to track infringement on systems that lack central servers. Gnutella presents a unique challenge to those clamping down on copyright infringement because unlike file-swapping systems such as Napster or Scour, Gnutella does not provide a central point through which people reach each other. Instead, the Gnutella systems pass along files through a giant daisy chain of individual computers. That means the MPAA must rely on ISPs to help it hunt alleged infringers. Harris Schwartz, Excite@Home's senior manager of network policy management, said the MPAA contacted the company and met its standards for notifying customers. "We're pretty strict about them providing us evidence," Schwartz said. He added that his company has received notices in the past from the entertainment industry, requesting that it help warn abusers of other networks. "Gnutella is kind of the next thing," he said. The MPAA said the crackdown is the result of a month-long investigation by Ranger Online, a company it hired to scour the Web and find cases of copyright infringement. The swapping of movies isn't nearly as widespread as music trading because films use so much bandwidth and can take hours to download. By notifying ISPs now, the MPAA is taking a more proactive stance than the music industry, which watched Napster use grow to the millions before it took legal action. "We are constantly looking at the other systems that are developing out there, and Gnutella was one of those," MPAA's Jacobson said, though he added that the organisation does not plan to go after individuals. So far, Gnutella hasn't attracted as much attention from the entertainment industry as other more widely used services such as Napster. Just last month, the Recording Industry Association of America, a music industry trade group that's led the successful charge to hobble Napster, said that Gnutella isn't creating enough of a threat to justify a crackdown because it's often difficult to use and it's networks are not as reliable. However, several analysts believed it was just a matter of time before the file-swapping system attracted legal heat. Shortly after the RIAA won its latest legal victory over Napster in appeals court, Gartner analyst P.J. McNealy predicted that the record industry would scratch Napster off the top of its list and pursue Gnutella. He said he was unsurprised that the film industry turned to Gnutella first. "It's kind of a natural flow of events," McNealy said. "The MPAA is sending a message it is not to be trifled with." Find out how the Internet is revolutionising the economy at the E-commerce Special. Have your say instantly, and see what others have said. Click on the TalkBack button and go to the ZDNet News forum. Let the editors know what you think in the Mailroom. And read other letters.