Hollywood has won its legal battle to prevent the spread via the internet of software that facilitates the decryption and copying of DVDs.

US District Judge Lewis Kaplan ruled in favour of action taken by several movie studios against the publisher of 2600, a magazine and website for hackers, after it posted on its website a software program, called DeCSS, which allows DVD movies to be decoded and played on Linux-based PCs.

Judge Kaplan said: "There is little room for doubting that broad dissemination of DeCSS threatens ultimately to injure or destroy plaintiff's ability to distribute their copyrighted products on DVDs. And, for that matter, undermine their ability to sell their products to the home video market in other forms."

Kaplan's 93-page ruling against 2600 is one of Hollywood's latest attempts to prohibit digital video piracy.

A Scandinavian programmer created the DeCSS software program which allows computers running Linux to play copy-protected DVDs. One compression technology, called DivX, included instructions for copying films and named DeCSS as a useful tool.

The studios sell DVDs that run on Windows-based PCs but did not develop the encryption technology for Linux, which spurred the development of DeCSS.

The judge also ruled that if website workers know the offending code is accessible at linked sites and supply the links to ease the spread of the code, they are in violation of the anti-trafficking provision of the Digital Millennium Copyright Act.

The judge called the publication's posting of the computer code "baseless" and at times compared it to a political assassination. Judge Kaplan said: "Computer code is not purely expressive any more than the assassination of a political figure is purely a political statement." The magazine had argued that posting of the DeCSS was protected under the First Amendment, an American's legal right to freedom of speech.

Jack Valenti, president of the Motion Picture Association of America, said in a statement that the court's ruling is a victory for consumers and for legitimate technology.

"Today's landmark decision nailed down an indispensable constitutional and congressional truth: it's wrong to help others steal creative works," he said.