The Google booth is seen at the 2006 Consumer Electronics Show in Las Vegas in this Jan. 5, 2006 file photo.

BEIJING, April 23 (Xinhuanet) -- An advertiser Tuesday filed a lawsuit against Google Inc., claiming it has been defrauding its AdWords customers by charging them for ads they don't want.

The advertiser in the case, David Almeida, had signed up for Google ads to promote his private investigation business in Massachusetts. Because he did not want to buy AdSense ads, Almeida said he left the maximum per-click bid blank, believing "optional" meant he could avoid the AdSense program by doing so.

Instead, it turned out the AdWords bid applied when he did not exercise that option, and he should have put "zero" into the box to opt out.

The lawsuit accuses Google of defrauding advertisers out of millions of dollars collectively by "redefining the universally understood meaning of an input form left blank." It was filed in U.S. District Court in San Jose, California, by Kabateck, Brown and Kellner, a law firm that has frequently filed consumer-protection lawsuits that seek multimillion dollar judgments or settlements.

"Most of the customers that actually fall victim to this scam are the unsophisticated advertisers," Kabateck said. "The sophisticated advertisers will know better, will know how to do it. These are the little guys that don't have money to lose on a program like this."

Google declined comment, saying it had not yet received the complaint.

The lawsuit is over Google's popular AdSense program, which targets ads to keywords in articles and other content at participating sites. The program complements the traditional AdWords program, which runs targeted ads alongside Google's search results. Ads under both programs generate the bulk of Google's revenues.