Microsoft has claimed the Harvard law professor appointed by a federal court to investigate an antitrust case against the company is biased and they claim the professor's own words prove it.

The US Justice Department wants a federal court to order Microsoft to stop forcing computer makers to include the company's Internet browser on machines that use Microsoft's Windows 95 operating system.

Judge Thomas Penfield Jackson has issued a temporary injunction to that effect, and plans to issue a final ruling in May. Jackson appointed Harvard professor Lawrence Lessig as a "special master" a temporary magistrate who assists in fact-finding.

Microsoft argued the inappropriateness of naming a special master in the case. And cited a June 1997 e-mail message allegedly sent by Prof Lessig to Mr Peter Harter, an attorney for Netscape Communications, Microsoft's chief rival in Internet browsers.

In the message, Prof Lessig describes his experience of installing the Microsoft Internet Explorer browser on his Apple Macintosh computer. "OK, now this is making me really angry," he wrote, adding that he discussed his problem with someone named Charlie Nesson, who suggested that Prof Lessig sue Microsoft.

Prof Lessig was upset because installing Internet Explorer changed settings on the Netscape browser he'd previously used.

"Instead of contacting Microsoft technical support. . . he contacted Netscape's lobbyist, the person who is leading the charge in Washington against Microsoft, and in his e-mail he basically compares loading a Microsoft product to selling his soul," said Microsoft spokesman Mr Mark Murray. "That would indicate at least a potential bias."

In a tart riposte, the Justice Department defended the judge's right to appoint a special master in the case and said Prof Lessig is amply qualified for the job.