"A business model built on infringement is not only morally and legally wrong, but it is also a threat to the development of the legitimate on-line music market," said Hilary Rosen, CEO of the Recording Industry Association of America (RIAA), in a statement. RIAA is the trade group that represents the U.S. recording industry organization.

"The Court's decisive and unanimous ruling today is a victory for all creators. The Ninth Circuit Court affirmed our legal position on every point," Rosen said.

Despite the court's ruling to the contrary, Napster is still maintaining that its MP3 file exchange is a type of "non-commercial use" allowed by the Audio Home Recording Act.

The court declined to state an opinion on the applicability of Napster's argument that it is an "Internet service provider," a type of organization that is shielded from copyright infringement suits by statutes of the Digital Millennium Copyright Act.

"We instead recognize that this issue will be more fully developed at trial," the opinion read.

The court also justified the injunction by anticipating that users would rush to download songs before trial if the service were to remain open.

Indeed, according to Webnoize.com statistics cited by CNN, an estimated 250 million songs were downloaded through Napster this weekend alone.

Harvard students contributed to the Napster frenzy, seizing what they feared would be their last opportunity to take advantage of the free program.