Microsoft won praise on Monday for its proposal to comply with interoperability demands by the European Union's antitrust watchdog, which said the plan would now be put to industry peers for their opinion.

The U.S. software giant could be hit with a fine of up to $5 million a day if the European Commission concludes that its proposals would not allow non-Microsoft work group servers to achieve full interoperability with Windows PC and servers.

But the EU executive voiced satisfaction, even though the sticky question of "open source" licenses was not fully resolved to the Commission's liking.

"I am happy that Microsoft has recognized certain principles which must underlie its implementation of the Commission's decision," European Competition Commissioner Neelie Kroes said in a statement.

In addition to agreeing to allow the development and sale of interoperable products on a worldwide basis, Microsoft has also recognized that "a category of the information which it is obliged to disclose" will be royalty-free.

However, the Commission said Microsoft considers that the software source code developed by recipients of interoperability information that implements the company's protocols should not be published under a so-called open source license.

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