Ex-Microsoft CEO and current Chairman Bill Gates is testifying Monday in US Federal Court in a seven-year-old $1 billion (£600 million) antitrust lawsuit by Novell.

Novell first brought the suit against Microsoft in November 2004, claiming Microsoft had purposefully misled Novell prior to the launch of Microsoft's Windows 95 operating system and, as a result, caused Novell to lose market share of its WordPerfect office suite. Novell argued that Microsoft's alleged trickery ran afoul of antitrust laws, according to court documents.

Novell had filed six claims against Microsoft, five of which were dismissed, with the US Court of Appeals reversing the dismissal of the sixth claim and moving the case back into district court.

Novell lawyers contend that Microsoft had invited Novell to work on a version of WordPerfect for the Windows 95 operating system. Gates directed Microsoft's engineers to reject Novell's application to make WordPerfect an official Windows application for the launch, according to Novell.

Microsoft was also selling its own office suite, Microsoft Office. After the release of Windows 95, sales of WordPerfect slowed dramatically. Novell later went on to sell WordPerfect to Corel, at a $1 billion loss.

Microsoft lawyers have argued that the version of WordPerfect for Windows 95 was defective and caused the operating system to crash. "We are confident Bill Gates' testimony will help show that Novell's claims have no merit," said Microsoft lead attorney James Jardine.

While both newer versions of Windows and the WordPerfect suite have subsequently released, the case is still important in that it could help clarify what obligations an owner of a dominant technology has to help potential competitors, said Bruce Schneider, an antitrust partner with the Stroock & Stroock & Lavan law firm. He is not involved in the lawsuit.

Attachmate purchased Novell last April, with the help of Microsoft, which acquired a number of patents in the deal.

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