The Fort Collins, Colo., company said it will remain a plaintiff in the case, but chose to withdraw as the lead "in order to concentrate our efforts in helping our clients develop their claims of click fraud."
"We remain a member of the class and our click fraud claims against Google will still be litigated when and if the class is certified," Scott Boyenger, Click Defense's chief executive, said in a statement Thursday.
A hearing on the motion to grant class-action status to the suit is set for May 2006 in U.S. District Court for the Northern District of California.
In filing the suit in June, Click Defense accused Google, based in Mountain View, Calif., of failing to take appropriate action to combat click fraud on the ads it sells. Nearly all of Google's revenues come from the money advertisers pay the search engine when a visitor clicks on the sponsored links accompanying search results.
Click fraud is a term used in the industry to describe the practice of clicking on ads without the intent to buy a product. The practice, which can be manual or automated, is sometimes used by competitors to increase the advertising cost of rivals. It's also used by unscrupulous ad publishers to boost revenues.
Google has denied any wrongdoing, and has a policy of identifying click fraud and crediting customers who have fallen victim to the practice.
"We have just received the motion papers and are reviewing them," Google spokesman Michael Mayzel said Friday of Click Defense's decision.
Click Defense, which filed the suit on behalf of Google customers, sells services for detecting click fraud and analyzing traffic on Web sites. The company said its decision to withdraw as lead plaintiff came "in light of a pending motion of another potential plaintiff to join in the action and act as representative plaintiff."
Clarence Briggs, chief executive of Advanced Internet Technologies Inc., a Fayetteville, N.C. provider of Web-hosting services to businesses, said his company decided to take over as lead plaintiff after losing "a great deal of money with Google" as an advertiser.
"I've asked for my money back, and they've ignored it," Briggs said. "I'm fed up."