Researchers headed by Princeton University professor Edward Felten filed the challenge in order to present their findings at a computer security conference in August.

Felten had originally planned to present a paper disclosing how his team defeated a digital-music antipiracy measure at another conference in April, but bowed out after the recording industry threatened a lawsuit.

Felten's team, which included students and professors from Princeton and Rice universities and an employee of Xerox Corp.'s Palo Alto Research Center, has been at odds with a music-technology consortium called the Secure Digital Music Initiative ever since they responded to a challenge to hack an SDMI copyright-protection measure last September.

The researchers claim to have successfully hacked the technology, but SDMI and the Recording Industry Association of America (RIAA), a music-industry trade group, have since sought to bar them from telling how they did it.

A lawyer associated with SDMI and the RIAA sent Felten a letter in April telling him he could face legal action under a 1998 law that bars efforts to defeat copyright-protection efforts.

The lawyer, Matthew Oppenheim, has since backed away from the letter, saying the SDMI had an obligation to protect the trade secrets of the companies that developed the anti-piracy technology but never intended to sue Felten.

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Felten told reporters on a conference call legal action was necessary to stop the music industry from interfering with the scientific process. Academics and other experts have a right to discuss their work, he said, and the public has a right to know if anti-piracy software is effective or not.

Publication of the group's findings would not affect the technology one way or the other, he said. "If deployed, the technology would likely be widely defeated quickly. We didn't cause that, and we're not going to change it," he said.

RIAA senior vice president Cary Sherman said Felten faced no legal threat and filed the motion to drum up publicity.

"Since we've said we have no issue with the publication of the Felten paper, they now resort to suing us to keep this issue alive," Sherman said in a statement.

The Electronic Frontier Foundation (EFF), a civil liberties group, filed the motion in New Jersey federal court against the two music-industry groups, the U.S. Justice Department and Verance Corp., one of the companies that developed the antipiracy effort.

EFF lawyers said they hoped the court would take a look at the constitutionality of 1998 Digital Music Copyright Act as well. Critics have said the law violates free speech by barring efforts to circumvent encryption technologies.