Timeline: Microsoft's battle with EU antitrust regulators

People use computers at a Microsoft retail store in San Diego January 18, 2012.

REUTERS - The European Commission imposed a 561 million euro fine on Microsoft on Wednesday for breaking a pledge to offer European consumers a choice of web browsers.

Here are some key events in Microsoft's relationship with EU antitrust regulators:

1998 - The European Commission opens an investigation into Microsoft over operating system interoperability issues, after a complaint from Sun Microsystems.

2000 - The Commission begins investigating the tying of Microsoft's Media Player with its operating system.

2004 - Regulators impose a 497 million euro fine on Microsoft for not making data available to rivals and for tying Media Player to its operating system.

2006 - The Commission levies an additional 280.5 million euro fine for Microsoft's failure to comply with the 2004 EU order to provide data to rivals.

2008 - Regulators open two new investigations, one into interoperability issues, and a second into browser choice.

2008 - The Commission imposes a 899 million euro fine, its second additional penalty, after Microsoft again fails to comply with the 2004 EU order.

2009 - Microsoft settles the 2008 investigation into browser choice with an offer to allow access to rival products.

2012 - Europe's second highest court reduces the 2008 fine to 860 million euros from 899 million euros, on appeal by Microsoft.

2013 - Competition regulators impose a 561 million euro fine for not complying with the 2009 promise on web browser choice.

Sources: European Commission, Microsoft

(Compiled by Foo Yun Chee; editing by Rex Merrifield and David Cutler)