Microsoft has filed a lawsuit in a patent fight involving Lucent Technologies, Gateway and Dell Computer after being asked to intervene because the products involved use its own technology.
Lucent filed a claim against Gateway last June, claiming that some Gateway products incorporating Microsoft technology infringed Lucent-owned patents. Lucent also targeted Dell with a similar patent suit last year.
In February Microsoft was ordered to intervene as a defendant and counterclaimant.
On Tuesday Microsoft filed a lawsuit requesting that the court declare invalid 13 patents that Lucent claims to hold. The patents cover audio and video coding as well as position-sensed stylus and touch-screen form-entry technology.
Microsoft said these patents were "not infringed and are invalid, and ... some are unenforceable".
Lucent responded a request for a jury trial.
"When we spoke to Microsoft about this, we said that we were asking for a fair return on our technology," Lucent spokeswoman Mary Lou Ambrus said. "Since the beginning of Lucent, we have always tried to maximise the value of our intellectual property."
Ambrus refused to comment further on the case, saying she would not speculate on what would happen next in the legal battle.
Microsoft was not immediately able to comment.