Google last week was sued by Web Tracking Solutions and Daniel Wexler for providing accounting information for its Internet ad publishers.

According to a complaint filed on July 31, Google's AdSense service violates Wexler's patent, "Third-party on-line accounting system and method therefor," which was filed on Oct. 11, 1996, and granted Sept. 28, 1999.

The patent describes a way to provide online accounting and statistical information about ads served by a third party -- Google, for example -- to a Web site on behalf of advertisers.

This marks the fourth time Google has been sued for patent infringement in 2008. In 2007, the company was named in 13 patent suits.

Google has long been a foe of frivolous patents and last year backed calls for patent reform. "Google and other technology companies increasingly face mounting legal costs to defend against frivolous patent claims from parties gaming the system to forestall competition or reap windfall profits," the company said in a blog post last year.

Whether or not Wexler's patent qualifies as such is a matter for the courts, but the Patent and Trademark Office appears to have narrowed its definition of what qualifies as a patentable software innovation, a change that should help Google as a defendant in patent cases.

In a recent post on University of Missouri law professor Dennis Crouch's blog, Patently-O, guest blogger John F. Duffy raises the possibility that Google may have a harder time enforcing its software patents because of the PTO-revised position on what's patentable.

Duffy observes in citing the Bilski case, which is currently being appealed, that the PTO "takes the position that process inventions generally are unpatentable unless they 'result in a physical transformation of an article' or are 'tied to a particular machine.' "

While this might invalidate some of Google's patents, it should also provide Google with a defense against patent claims such as Wexler's.

Google got some good news in an unrelated case on Friday. The lawsuit filed by a former Google contractor claiming that the company stole the idea for Google Sky was dismissed.