The European Commission has fined Microsoft €280.5 million for failing to comply with the terms of a March 2004 antiitrust judgement against it.

Microsoft has already paid a €497 million fine as a result of the judgement, in which the Commission found that Microsoft had used its near-monopoly in the PC operating systems market to gain advantage in the markets for work group server operating systems and media players.

At the time, the Commission ordered the company to release a version of Windows XP without a built-in media player, and to provide its competitors with technical details of certain communication protocols used by its server products.

The €280.5 million fine announced today is to punish the company for failing to provide those technical details in a timely manner. If Microsoft continues to fail to comply, the Commission will increase the amount of the daily fine to €3 million per day, it said.

Microsoft has called a press conference this afternoon to discuss the decision.

The Commission initially gave Microsoft 120 days to disclose details of the software interfaces used by its server products to communicate with the desktop versions of Windows, so that competing vendors could build compatible systems. Progress was slow, and in March last year, and then again in June, the Commission threatened the company with additional fines if it didn't fully comply with the ruling.

Microsoft succeeded in pushing back the deadline numerous times as negotiations continued, but the Commission remained unsatisfied with Microsoft's progress, notably in documenting its software interfaces.

Microsoft is due to submit the final batch of technical documentation required by the Commission by 18 July, according to a timetable the two parties agreed with the independent monitoring trustee appointed to oversee matters.

The Commission had earlier threatened fines of up to €2 million a day until all the required information about the communications protocols had been supplied. The €280.5 million figure is based on a fine of €1.5 million per day, for the period from 15 December to 20 June.

In a separate action, Microsoft has also appealed against the anti-trust ruling itself. The European Court of First Instance in Luxembourg finally heard that appeal in late April, and is now considering its decision.