The European Commission's investigation was prompted by complaints from Microsoft rivals in the European Committee for Interoperable Systems.
Europe's competition watchdog has launched two new antitrust investigations into Microsoft's business practices.
The European Commission said in a statement Monday that it's eyeing the possibility that the company is violating monopoly laws by failing to make its products interoperable with competitors' offerings and by illegally bundling its Internet Explorer Web browser with the Windows operating system.
"The initiation of proceedings does not imply that the Commission has proof of an infringement. It only signifies that the Commission will further investigate the case as a matter of priority," the EC said.
The EC said it launched the investigation into Microsoft's interoperability practices following a complaint from Microsoft rivals that have banded together in a group called the European Committee for Interoperable Systems. ECIS comprises Sun Microsystems, Adobe, IBM, Oracle, Red Hat, and several other vendors that compete with Microsoft in the software market.
"Microsoft continues to use its desktop monopolies to restrict competition," said an ECIS spokesman, in a statement.
The group claims Microsoft has refused to release the documentation its members need to make their products work with Microsoft Office and the .Net Framework programming environment.
The EC's probe of Microsoft's bundling of Explorer and Windows arose from complaints by Norwegian browser developer Opera Software -- also a member of ECIS.
The investigations mirror earlier EC actions against Microsoft.
October, the company said it would not appeal $1 billion in antitrust fines levied by the EC after the Commission found the company guilty of withholding interoperability information and illegally bundling Windows Media Player software with the Windows OS.
At the same time, EC commissioner Neelie Kroes said Microsoft had come into full compliance with European competition rules after it agreed to reduce fees for interoperability documentation and produce a version of Windows without Windows Media Player for distribution on the Continent.
In a statement Monday, Microsoft said it would "cooperate fully" with the EC in the latest investigations.
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