Microsoft must pay $1.4 billion to the EU following on from a failed appeal in an antitrust case late last year.
The European Commission has now fined the computing giant after it determined that Microsoft has defied sanctions imposed on it for anti-competitive behaviour - a ruling that Microsoft appealed and lost.
Microsoft must now pay around £680.9m finally bringing to an end an antitrust case that has been rolling on since 2004.
In that year, an EC investigation determined that Microsoft was guilty of freezing out rivals by not releasing details to developers of server software and products such as media players.
The EC ordered Microsoft to pay 497 million euros for abusing its dominant market position.
The European Court of First Instance upheld this ruling last year.
However, Microsoft appealed this decision, lost and then failed to act.
"Microsoft was the first company in 50 years of EU competition policy that the Commission has had to fine for failure to comply with an antitrust decision", competition commissioner Neelie Kroes said in a statement.
Microsoft is now expected to fork out the fine but has, in its statement in response to the EC fine, pointed to its decision to open up its software to other developers.
"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", it said in a statement.