The company said on Friday that it is seeking more than $1bn in damages from Microsoft for making its Windows XP operating system incompatible with Sun's Java programming language.

Any lack of consumer acceptance of Java is due to Sun's own failures and not to actions by Microsoft

Microsoft spokesman

Sun claims that by locking the language out of the widely-used XP system, Microsoft has slowed the take-up of Java by programmers.

The company also argues that the exclusion of Java has made it more difficult to use competing products alongside Microsoft's dominant software.

Compensation claim

"This private antitrust lawsuit is intended to restore competition in the marketplace by removing unlawful barriers to the distribution of the Java platform, and to interoperability between Microsoft software and competitive technologies," said Sun senior vice president Michael Morris.

"What is at stake here is the future of an open software industry and an open internet."

Mr Norris said Sun had suffered commercial damage amounting to "north of a billion" as a result of Microsoft's tactics.

Sun also wants the courts to force Microsoft to distribute the most recent versions of Java with its Windows XP system in future.

Sun designed Java to work on all kinds of computers, irrespective of which operating system they run. The company had intended it to become the most widely used programming language.

Microsoft rebuttal

But Microsoft has denied holding back the take-up of Java by programmers.

"Any lack of consumer acceptance of Java is due to Sun's own failures, and not to actions by Microsoft," a spokesman said.

This is not the first time that Sun and Microsoft have crossed swords over Java.

Last year, the software giant paid Sun $20m to settle a lawsuit brought after Microsoft created a version of Java that was compatible only with Windows.

Sun's shares were trading 13% higher at $9.97 late on Friday, buoyed in part by news that the company expects to hit sales targets.

Microsoft shares were up $1.22 at $63.94.

Government example

Sun's lawsuit follows a similar challenge from AOL Time Warner, which in January sued Microsoft for allegedly forcing licensees of its dominant Windows operating system to use Microsoft's own Explorer browser.

AOL claims that this strategy unfairly displaced its Netscape browser as the most widely-used internet search tool.

Sun and AOL's private lawsuits both take their cue from the outcome of the US government's anti-trust action against Microsoft last year.

In that case, an appeal court decided last June that Microsoft had engaged in anti-competitive behaviour, but overturned an earlier ruling that the software giant should be broken up.

Nine US states and the District of Columbia are still in court pressing for tougher penalties against Microsoft.

On Friday, a US judge agreed to delay the next round of hearings, originally pencilled in for 11 March, by one week.