The mediator in Microsoft Corp's antitrust trial met parties in the case in Chicago, for the third Monday in a row, sources said.

Judge Richard Posner, chief of the United States Court of Appeals for the Seventh Circuit, who is acting in a private capacity, is mediating the case.

US District Court Judge Thomas Penfield Jackson - who is trying the case in Washington - asked Judge Posner to step in to mediate the case after earlier attempts at settlement failed.

Judge Jackson has already found that Microsoft used monopoly power to harm consumers, competitors and other companies. He has now to decide whether those actions violated the law.

Last week the Justice Department and 19 states filed a 70page brief alleging that Microsoft violated antitrust law in at least four different ways. The assertion that Microsoft broke the law was based on the judge's findings of fact.