A European court has upheld a 2004 antitrust decision against Microsoft in a ruling that may force the software behemoth to change its business practices.

The Court of First Instance ruled that the European Commission was right in finding that Microsoft abused its dominant market position in software by bundling applications to its Windows operating system and by refusing to divulge information about Windows to rival developers of applications. The court also upheld $690 million in fines against Microsoft.

While Microsoft had argued that the commission had erred, the court rejected the appeal, saying: "The court finds that the arguments put forward by Microsoft in the alternative are unfounded and, in particular, that Microsoft has not shown that the commission erred in assessing the gravity and duration of the infringement or in setting the amount of the fine."

The court, however, did reject the European Commission's creation of a trustee to monitor Microsoft.

The ruling is expected to be appealed by Microsoft to the European Union's highest court, the European Court of Justice, but an appeal may be made only on points of law and not of fact. Microsoft has two months to appeal.

The European action echoed the Justice Department's antitrust case against Microsoft, which was prompted by the complaints that Microsoft was abusing its dominant position to keep the Internet browser Netscape off personal computers. That case was settled in 2001.

With the court's ruling, European antitrust regulators may now have the legal tools to take a more aggressive stance against perceived anticompetitive practices by companies doing business in Europe.

"They will apply to any dominant company that engages in the same behavior," Michael Reynolds, of law firm Allen & Overy, told the BBC. "It's not just about Microsoft."

The ruling, he said, "provides legal certainty now as to what you can and you can't do in relation to information you have to make available to companies who compete in your environment to enable them to be a viable competitor."