The decision is a major blow to the software giant and its boss, Bill Gates, and is a significant success for one of its few major competitors, Sun Microsystems. It comes as Microsoft also faces assault from the US government, who accuse it of using its muscle to get rid of competition.
Sun produces a piece of rival software called Java which enables programmes to run on any system. This undermines Microsoft's dominance which is built on persuading all manufacturers and consumers to use its Windows operating system. Java is used by software designers producing programmes for users.
In an effort to tackle the problem, Microsoft licensed the Java software, then redesigned it so that it would only run on Windows, said Sun.
The judge, Ronald Whyte said Sun was "likely to prevail on the merits" of its lawsuit. In a preliminary injunction, he gave Microsoft 90 days to modify both Windows 98 and Internet Explorer. If it has not altered them by that date, then it will have to pull the products off the market altogether. Microsoft said that it would comply. The order does not affect software already shipped.
Microsoft spokesman Jim Cullinan said the company would "take the necessary steps to comply," but he added: "We believe Sun's legal strategy is shortsighted and is trying to deny customers and developers the choice of the best Java implementation in the marketplace."
In the separate federal case in Washington that is probing Bill Gates tactics against his competitors, the court heard of Mr Gates fears that Java would damage him. In a memo to Microsoft executives about IBM, Mr Gates warned that "the Java religion coming out of the software group is a big problem".
The court in California heard that Microsoft formed a special group of programmers to try to gain control over Java. But other executives were worried. "I believe that our true goal, controlling the future of Java, will be totally transparent and mostly unacceptable" to other manufacturers, said one.Reuse content