"We have seen numerous reports of click fraud estimates which we believe significantly overestimate the impact on advertisers," the search firm stated.
"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 (eg 14 per cent), which is troubling."
Click fraud involves individuals using scripts or manually clicking on pay-per-click advertisements for financial gain.
A company could click on advertisements to deplete its competitor's marketing budget, for instance, and a website operator could be tempted to commit click fraud to increase revenues.
The 17-page report noted that only a few advertisers actually rely on third-party auditing firms, but that their findings have been widely publicised.
The search firm fears that advertisers will adjust their strategies based on the reports, causing their online campaigns to become less effective.
The main cause of the faulty research is what Google referred to as " fictitious clicks", events that were reported as fraudulent, but which never showed up in Google's logs as clicks.
Fictitious clicks can be caused when a user reloads a website, when a user hits the browser's back button or opens up a new browser window.
Auditing systems in each of these cases can detect a fraudulent click although the visitor only once clicked on an online ad.
A second cause of incorrectly measured clicks can be the mixing of advertisers and ad networks on a single site, Google charged.
The search firm acknowledged the need for independent click fraud audits. The company joined the IAB Click Measurement Working Group last week to establish industry-wide definitions of advertising clicks.
Mikhail Ledvich, a spokesman for ClickFacts, confirmed Google's findings, but added that the report used data that was collected in February.
Clickfacts has since made changes to its technology and did not see a significant change in the amount of fraudulent clicks.
"The difference wasn't significant enough to say that this was seriously impacting our accounts," Ledvich told vnunet.com.
In an email to vnunet.com, Adwatcher claimed that several points of Google's criticism did not apply to its technology and argued that Google failed to properly test its results.
"It seems that the study is very limited in scope," the company said.
"We consider our methods to be very reliable. However, we are always working on improving them and we welcome any suggestions that our customers could benefit from."
Click Forensics did not immediately respond to a request for comment.
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