After spending 3 years appealing against the verdict, Microsoft has finally agreed to start complying with a European Commission 2004 anti-monopoly ruling against it.
Microsoft was found guilty of shutting out rivals from Windows in order to gain a larger share of the market.
The company will now give third party program developers access to information that will allow them to make systems interoperable with Windows, and cut the fees it charges for this.
Microsoft had taken its appeal to the European Court of First Instance, but it upheld the Commission's judgement that Microsoft had abused its dominant market position.
The court also upheld the Commission's record £343 million fine against the US company.
"I welcome that Microsoft has finally undertaken concrete steps to ensure full compliance with the 2004 decision", said Ms Kroes of the Commission.
"It is regrettable that Microsoft has only complied after a considerable delay, two court decisions, and the imposition of daily penalty payments."