The EU General Court has decreased an anti-trust fine first issued against Microsoft in 2008 but dismissed the company's appeal against the overall ruling.
While maintaining it "essentially upholds the Commission's decision" the EU General Court chose to reduce the fine from its initial fee of €899m to €860m.
The company first fell foul of anti-trust regulators in 2004, when it was fined €497m for using its PC software market dominance to block competitors.
Specifically, the European Commission (EC) claimed Microsoft's refusal to release code that could have been used to by other companies to create products compatible with its own was stifling innovation.
Alongside the fine the ruling ordered Microsoft to make its server software code available to competitors so their products could work alongside it.
The EC later added a further fine in 2008 after it ruled Microsoft had failed to comply with the order.
At the time of publishing Microsoft had not responded to V3's request for comment on the ruling.
EC vice president Joaquín Almunia issued a statement praising the court's decision.
"Today's judgement fully vindicates the enforcement action that the Commission took to ensure Microsoft's compliance with its obligations," he said.
"The ruling confirms that Microsoft did not comply with the Commission's decision and that the Commission was right to impose a penalty, even though the Court chose to slightly reduce the amount of the penalty payment from €899m to €860m."
The EU is also currently considering an anti-trust investigation into Google. Most recently EU competition commissioner Almunia said its initial investigations had identified four areas of concerns over Google's businesses practices.
Following the ruling Bruce Kilpatrick, head of the competition law team at legal firm Addleshaw Goddard, said the court's decision should act as a warning to Google.
"The court agreed with the Commission that Microsoft had failed to allow its competitors access to interoperability information on reasonable terms, and largely upheld the penalties imposed for every day that Microsoft did not comply with its ruling," said Kilpatrick.
"This amounted to a huge sum and other technology companies currently embroiled in anti-trust disputes, including Google, will be taking note."