Google's AdWords program has come under attack from a familiar foe, according to an InformationWeek story, which details a potential class-action lawsuit that charges the search giant with fraud.

The suit was filed by Kabateck Brown Kellner, LLP, the same law firm that represented plaintiffs in Advanced Internet Technologies v. Google. That case eventually became part of a $90 million click fraud settlement.

In the current suit, Kabateck Brown Kellner, which represents David Almeida, is trying to get certification to proceed as a class action. If that maneuver is successful, Google could potentially face a class as large as its total AdWords customer base.

At issue is whether Google failed to make clear that to avoid running ads on its AdSense network, customers must enter a zero in the appropriate box, rather than leaving it blank. According to the lawsuit, Google has charged a number of advertisers for ads they never intended to buy.

"This affects the most unsophisticated customers the most," the plaintiffs' lawyer Brian Kabateck said. "By redefining the universally understood meaning of an input form left blank, and then intentionally concealing this redefinition, Google has fraudulently taken millions of dollars from Plaintiff and the members of the class."

The case was filed in the U.S. District Court in San Jose, Calif.

Google had no comment on the case.