Microsoft was fined a record €899 million (£683 million) by the European Commission yesterday as it received its third financial penalty for failing to comply with a landmark antitrust ruling issued four years ago.

As the battle between the American software giant and European regulators enters its tenth year, Microsoft has now been fined almost €1.7 billion for abusing its dominance of PC operating systems through its Windows software.

Announcing the largest fine on a company, Neelie Kroes, the EU Competition Commissioner, said: “I hope today's decision closes a dark chapter in Microsoft's record of non-compliance.”

Under the ruling of March 2004, Microsoft was instructed to make complete and accurate interoperability information available on reasonable terms to competitors so that they could develop their own operating systems for servers.

However, until it forced the company to introduce its present fee structure last October, the Commission considered that the rates Microsoft was charging were far from reasonable. As a result, the fine is based on the 15-month period of non-compliance before that date and is considerably larger than the original €497 million penalty the company initially received.

Pointing out that the fine could have been as high as €1.5 billion, Mrs Kroes said: “This should be a signal that we will stick to our line.”

Microsoft said that it would review the decision. If it decides not to appeal, a line will have been drawn under the original Commission ruling.

However, Microsoft will have to update the interoperability data it makes available continuously and licensees may lodge complaints if they believe that they are being unfairly treated.

Microsoft's fractious relationship with Brussels regulators is far from repaired. Last month the Commission opened two further investigations in a case which, with its implications for the range of internet browsers, some experts believe is potentially as big as, if not bigger than, the earlier one.

The inquiries, involving different Microsoft products, were prompted after Mrs Kroes received complaints that the company had unfairly tied its web browser, Internet Explorer, to its Windows operating system, and was making it difficult for competitors to work with Windows by not disclosing sufficient interoperability information.

EU fines on Microsoft

March 2004 Abusing its dominant position: €497 million

July 2006 Failure to comply with March decision: €280.5 million

Feb 2008 Charging rivals unreasonable fees: €899 million

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