File-swappers who distribute a single copy of a prerelease movie on the Internet can be imprisoned for up to three years, according to a bill that President Bush signed into law on Wednesday.

The Family Entertainment and Copyright Act, approved by the House of Representatives last Tuesday, represents the entertainment industry's latest attempt to thwart rampant piracy on file-swapping networks. Movies such as "Star Wars: Episode II," "Tomb Raider" and "The Hulk," have been spotted online before their theatrical release.

The law had drawn some controversy because it broadly says that anyone who has even one copy of an unreleased film, software program or music file in a shared folder could be subjected to prison terms and fines of up to three years. Penalties would apply regardless of whether that file was downloaded or not.

In a statement, Motion Picture Association of America president Dan Glickman said he wanted to "thank the congressional sponsors of this legislation for their strong advocacy for intellectual property rights."

The Family Entertainment and Copyright Act also includes sections criminalising the use of camcorders to record a movie in a theatre, and authorising the use of technologies that can delete offensive content from a film.

"The protection of intellectual property rights is vital to the movie industry," said Lamar Smith, a Texas Republican who joined Bush for the signing ceremony. "This bill is necessary to ensure that all those involved in the production of a film, from the director to the set carpenter, are not cheated."

The law's stiff penalties apply to "audiovisual" works, music and software that are "being prepared for commercial distribution." It's not clear how that would apply to fans who redistribute video files of TV shows aired in other countries first, or movies like Shaolin Soccer and Japanese anime flicks that can take years to arrive in the US market.

While some public interest groups have criticised the measure, others characterised it as a modest expansion to a 1997 law that made copyright infringement a crime -- even when no money changed hands.

Eric Goldman, who teaches copyright law at Marquette University Law School, said that the Justice Department will likely wield its new criminal enforcement powers responsibly. "I'm not as outraged by the (new law) as I expected to be," Goldman wrote last week.