Microsoft ( MSFT) can't quite get free of its lingering antitrust problems. The latest: Attorneys for plaintiffs in an Iowa class-action suit say the giant software maker is not complying with a landmark 2002 settlement with the Department of Justice.

Microsoft, says co-counsel Kent Williams of Minneapolis, has failed to open up its source code and reveal the underlying interfaces needed by developers to make their software compatible with Windows, as is mandated by the settlement.

An Iowa judge has given Williams permission to send information about the allegedly undocumented application programming interfaces to the DOJ, and Williams expects to do so late Monday. What action the department could take if it finds that that claim is true is unclear.

Williams' case is one of the few class-action suits against Microsoft that has yet to be settled. Interestingly, the case contains information on Microsoft's actions through the middle of 2006, while other cases focused on much older actions.

Known as Comes vs. Microsoft, the Iowa case alleges that the company deliberately misled the marketplace by announcing Vista, the new version of Windows, several years before it was actually ready to ship. It seeks damages to buyers who were allegedly overcharged.

"Vaporware," as announced-but-unavailable products are called within the industry, can be used as a tactic to freeze purchases of rival software and can be construed as an attempt to unfairly stifle competition. Indeed, the business version of Vista didn't ship until November of last year, and the consumer versions won't ship until next week.

Microsoft has historically been reluctant to open its source code, claiming that it would give its competitors an unfair advantage.

Microsoft spokesman Jack Evans said his company is in full compliance with the decree and "has documented everything it is required to document." Moreover, its compliance has been "exhaustively reviewed by both the Department of Justice and its technical committee."

In recent trading, shares of Microsoft were off 52 cents, or 1.8%, to $30.59.

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