Microsoft has filed a counterclaim in Sun Microsystems' private antitrust lawsuit against the software giant, with Microsoft claiming that Sun broke a contract that allowed Microsoft to distribute its own version of Java.

The 51-page counterclaim, filed Friday with Judge Frederick Motz in the U.S. District Court inMaryland, says that after a Sun lawsuit settled in January 2001 the two companies had an agreement for Microsoft to distribute its version of the Java Virtual Machine through 2008. Microsoft doesn't ask for a specific dollar amount in its counterclaim, suggesting instead that be determined at trial.

Sun's current lawsuit claims that Microsoft has tried to kill developer interest in using Java by distributing its own version that is incompatible with the version of Java controlled by Sun. Microsoft's goal, Sun lawyers claim, was to confuse developers and drive them to use Microsoft's .Net platform instead of Java.

Microsoft, in Redmond, Wash., claims Sun's alleged breach of contract has prematurely stopped Microsoft from using its Java license and "deprived Microsoft of the quiet enjoyment of technology it licensed" under the 2001 settlement agreement. The counterclaim accuses Santa Clara, Calif.-based Sun of "bad faith" dealings with Microsoft.

"For nearly a decade, Sun has instigated lawsuits against and governmental investigations of Microsoft based on alleged violations of antitrust and copyright laws in an effort to impede Microsoft's competition with Sun in the marketplace," Microsoft lawyer Matthew Larrabee wrote in the counterclaim. "Sun has no product strategy to counter Microsoft's investment in creating innovative and useful software, and therefore attempts to obstruct Microsoft through litigation."

Sun's Lee Patch, vice president of legal affairs, said the company is conducting a thorough review of the counterclaim. "We look forward to bringing evidence to prove the merit of all of our claims and answer Microsoft's counterclaims at trial," he said in an e-mail statement.

Motz is presiding over a number of private antitrust lawsuits against Microsoft. On Dec. 23, he ruled that Microsoft must distribute Sun's version of Java with Windows XP and by download, but Microsoft appealed that order, and the U.S. Court of Appeals for the Fourth Circuit, in Richmond, Virginia, delayed Motz's Java order on Feb. 3. The appeals court is scheduled to hear oral arguments on the "must-carry" Java order on April 3.