Microsoft has filed an appeal against the latest anti-trust fine imposed on it by the European Commission.

The Commission, Europe's top competition authority, fined the software maker €280.5 million (US$356 million) in July failing to comply with its 2004 antitrust ruling.

"Microsoft filed the appeal yesterday, as it said it would back in July," said Tom Brookes, Microsoft's spokesman in Brussels.

The Court of First Instance in Luxembourg is already considering Microsoft's appeal of the 2004 ruling, which ordered it to sell a version of Windows in Europe without its media player software, release some of its server protocols to competitors, and pay a fine of almost €500 million.

The court is likely to rule on the first appeal towards the end of this year or in the first half of next year. A conclusion to the latest legal challenge is likely to be years away.

Microsoft has claimed from the beginning that it is committed to honouring the Commission's 2004 anti-trust ruling. It paid the fine promptly and has offered a second version of Windows XP without Windows Media Player, although sales of that version have been almost non-existent.

The Commission has been more concerned about what it sees as Microsoft's failure to submit the required protocol information. In July its patience ran out. Announcing the €280.5 million fine, the European Commissioner in charge of competition, Neelie Kroes, said the documentation the company had submitted "fell significantly short of what was required".

Microsoft submitted new information to the Commission shortly after that, which the Commission is still studying.

Kroes has said she is confident that Microsoft's "foot-dragging" is over. "They are making constructive efforts now," she said, adding: "It's a shame they didn't do so two years ago."

To deter any further deliberate delays in complying with the 2004 ruling, the Commission has increased the future fines for failing to comply. The €280.5 million fine was calculated using a daily fine of €1.5 million from Dec. 16 last year to June 20, the day on which Microsoft made a more concerted effort to comply, according to the Commission.

Meanwhile, European anti-trust officials have been busy studying Windows Vista, the next version of Microsoft's operating system due to go on sale later this year and early next.

They are concerned that some new features in Vista may break the same antitrust laws that formed the backbone of the 2004 ruling. Microsoft has warned that Vista's launch could be delayed in Europe due to problems with European regulators.