Kazaa has vowed to appeal after an Australian court ruled that the internet file-sharing operator has infringed the country's copyright laws.

The Federal Court of Australia found that Kazaa violated Australian copyright law by authorising users to infringe music companies' copyright in recordings. The court ordered that the P2P firm must install filters to prevent future violations.

Ian Fogg, a broadband analyst at Jupiter Research Europe, said: "This is yet another battle in a long running war, but it's almost yesterday's fight because Kazaa is not as popular as it used to be and many downloaders have moved to BitTorrent and the e-Donkey networks.

"In terms of the bigger picture this is significant because it is an example of the general legal pressure coming to bear on such services and the fact that their options are being closed down."

Sharman Networks, the company behind Kazaa, said that it will appeal against the verdict.

"While the judgment has yet to be studied in detail, Sharman Networks is obviously disappointed with the decision," the company said in a statement. "We will appeal this decision vigorously and are confident that we will win on appeal.''

The case was brought by the Australian unit of Universal Music Group, part of Vivendi Universal, and other music industry plaintiffs, against Sharman Networks and other defendants.

"Despite the fact that the Kazaa website contains warnings against the sharing of copyright files, and an end-user licence agreement under which users are made to agree not to infringe copyright, it has long been obvious that these measures are ineffective to prevent, or even substantially to curtail, copyright infringements by users," the judge said in a summary of the decision.

The judge ordered that, within two months, the Kazaa software must have filters that exclude copyrighted works, and that Kazaa must apply "maximum pressure'' on existing users to upgrade to the filtered system.