Microsoft must now pay a record 899m euros ($1.4bn; £680.9m) after it failed to comply with a 2004 ruling that it abused its position.

The ruling said that Microsoft was guilty of not providing key code to rival software makers.

EU regulators said the firm was the first to break an EU anti-trust ruling.

The fines come on top of earlier fines of 280m euros imposed in July 2006, and of 497m euros in March 2004.

"Microsoft was the first company in 50 years of EU competition policy that the Commission has had to fine for failure to comply with an antitrust decision," Competition Commissioner Neelie Kroes said in a statement.

Future improvements?

An investigation concluded in 2004 that Microsoft was guilty of freezing out rivals in products such as media players, while unfairly linking its Explorer internet browser to its Windows operating system at the expense of rival servers.

The European Court of First Instance upheld this ruling last year, which ordered Microsoft to pay 497m euros for abusing its dominant market position.

DISPUTE TIMELINE March 2004: EU fines Microsoft 497m euros and orders it to release key Windows code to rival software developers September 2004: Microsoft tries to have the ruling temporarily suspended April 2006: Microsoft appeals the ruling in the European Court of First Instance September 2007: Microsoft loses its appeal

Last week, the firm announced that it would open up the technology of some of its leading software, including Windows, to make it easier to operate with rivals' products.

"As we demonstrated last week with our new interoperability principles and specific actions to increase the openness of our products, we are focusing on steps that will improve things for the future," Microsoft said.

Further cases

But the firm is still being pursued by Brussels.

Last month, the European Commission launched two new anti-competition investigations against Microsoft into similar issues.

The first will look at whether there are still problems regarding Microsoft abusing its dominance of the PC market to grab market share of the internet.

The Commission will also investigate the continued interoperability of Microsoft software with rival products.