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 releases. 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.