Portable navigation company TomTom, recently sued by Microsoft for patent infringement, has countered with its own lawsuit alleging that Microsoft's Streets & Trips product infringes on TomTom's patents. The suit (PDF, 8 pages) cites four patents and says Microsoft's use of the technology "has been and continues to be willful and without license from TomTom."

Microsoft last month sued TomTom for violation of eight of its patents. The case has received widespread attention in part because some of the technology in dispute involve TomTom's implementation of the Linux kernel -- the first time Microsoft has filed patent litigation over the open-source operating system.

"We are reviewing TomTom's filing, which we have just received," said Horacio Gutierrez, Microsoft deputy general counsel, in a statement released by the company today. "As has been the case for more than a year, we remain committed to a licensing solution, although we will continue to press ahead with the complaints we initiated in the U.S. District Court for the Western District of Washington and the International Trade Commission."

TomTom's suit, filed March 16, was first reported today by Bloomberg News.