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is taking aim at third-party researchers who are making what it calls unfounded claims about the extent of click fraud.

In a 17-page report released in conjunction with the Search Engine Strategies conference, Google argues that findings by some outside firms are flawed and misleading.

"We're trying to find ways where we can give information to advertisers that is truthful,'' Schmidt told the Search Engine Strategies conference Wednesday, adding that the company had click fraud "under control."

Click fraud is a big concern for Wall Street, since most of Google's revenue comes from pay-per-click advertising on its AdWords network. Until now, Google has stressed to advertisers that it takes the issue seriously and to investors that it doesn't have an impact on its bottom line. Now, the gloves have come off.

"We have continued to see third-party click fraud auditing firms stating that their measurements show much higher levels of click-fraud than we believe could possibly be realistic,'' says the report, referring to estimates of 14%. "Although only a very small number of AdWords advertisers use third-party click fraud auditing firms, the click fraud estimates produced by these firms have been highly publicized and caused concern for many advertisers. We also receive click fraud auditing reports generated by these firms requesting refunds.''

Click fraud occurs when someone clicks on the ads of a competitor to drive up their costs. Publishers also improperly hit the ads on their own Web sites to improperly boost their revenue.

Google, which picked apart the reports of outside firms such as ClickFacts, AdWatcher and Outsell, won't provide any data about the extent of click fraud on its network, claming that doing so would help crooks. That argument is rejected by the researchers.

Though Google continues to say that it intercepts most improper clicks and recently beefed up its monitoring tools, the issue won't go away. Wall Street analysts say that concern about click fraud weighs down Google shares, which have declined 8% this year despite a blowout second quarter and potentially promising deals with

News Corp.'s

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"The good news here is that the debate has been moved,'' says Chuck Richard, a vice president at Outsell, who has defended his company's estimates against Google's criticism. "It would help their own cause if they would increase their own transparency.''

But during a discussion with moderator Danny Sullivan, Schmidt pointed out that the company doesn't provide details on financial operations "to the frustration of many."

"We have a whole bunch of people who are trying to reverse engineer the economics of Google,'' Schmidt said.