Microsoft said today it has posted more than 14,000 pages of software code online as a response to an European Commission anti-competition decision last month.
February's €899m (£681m) fine took the firm's total liability to €1.68bn (£1.27bn) for abusing its dominant market position.
A 2004 order from Brussels (PDF) required the company to provide information to competitors so that their software could run on its operating systems – but it has failed to do so until now.
The underlying code, or protocols, are built into Microsoft Office 2007, Microsoft Office SharePoint Server 2007 and Microsoft Exchange Server 2007.
Microsoft has committed to publishing a further 30,000 pages of code, though it has not set out a timetable.
Over the weekend Microsoft announced plans to develop a unified security management platform for businesses, known as 'Stirling'.