The European Commission has given Microsoft a 899 million euros (approx. $1.4 billion) fine because the software giant wasn't willing enough to share key code of Windows to rival software makers.
The new fine comes on top of 280 million euros and 497 million euros fines imposed in July 2006 and March 2004, respectively. Competition Commissioner Neelie Kroes claims Microsoft was the first company in 50 years of EU competition policy that the Commission has had to fine for the failure to comply with an antitrust decision.
An investigation concluded in 2004 that Microsoft was guilty of freezing out rivals in products such as media players, while unfairly 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.
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.
But the firm is still being pursued by Brussels.
Earlier this 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.