The European commission's latest fine - the largest ever levied against one company - brings the total amount that Brussels has extracted from Microsoft for anti-competitive behaviour to €1.68bn (£1.27bn) over the past four years.

The fines relate to the commission's original investigation, concluded in 2004, into the way the company controlled access to its Windows operating system. The commission demanded that Microsoft 'unbundle' its Media Player application from Windows so that rival applications can be used to listen to music or watch videos online.

The commission also demanded that Microsoft give makers of rival software used by companies on the servers that run their internal networks enough information about Windows so they can work with desktop computers running the Microsoft operating system.

An estimated 95% of desktop computers run on Windows worldwide while roughly four out of five corporate servers are using some form of Windows architecture, giving Microsoft a dominant position in the market.

The commission became frustrated at the company's slowness in implementing the 2004 ruling - which was accompanied by a €497m fine - and in 2006 it imposed a daily fine on the company that added up to a further €280.5m.

While Microsoft has complied with the unbundling ruling, the company moved to charge a royalty for the information needed by developers of rival server software. After further legal wrangling with the company the commission ruled last year that these charges were unreasonable.

Microsoft has reduced the royalty fees but the commission ruled today that it had only been charging the correct amount since October last year - three years after the original judgment.

Initially, Microsoft charged a royalty rate of 3.87% of a licensee's revenues for a full Windows patent licence and 2.98% for a licence that gives access to the so-called 'interoperability information' needed to make rival software compatible with Windows. In May last year, Microsoft dramatically dropped its prices for rivals within the EU to 0.7% for a patent licence and 0.5% for the interoperability information while its worldwide prices remained the unchanged.

Finally in October Microsoft started offering a worldwide patent licence for 0.4% and giving out its interoperability information for a flat fee of €10,000. Only at that point, the commission said Wednesday, did Microsoft actually comply with the 2004 judgment.

Last month the commission announced two further formal investigations into Microsoft into alleged abuse of its dominant market position, following complaints from the European committee for interoperable systems and a Norwegian company Opera Software.

The commission is looking at whether Microsoft illegally refused to give rivals access to interoperability information from its suite of Office and .NET products. The commission is also looking at the way Microsoft ties together Windows and its Internet Explorer browser.