Recent data from Click Forensics found that an average of 14.2 percent of clicks were fraudulent in the last quarter of 2006.

Google maintains that fraudulent clicks are but a fraction of a percent, and that the click-fraud study was flawed.

Google's Shuman Ghosemajumder says the firm was "making basic counting mistakes and inflating the number of clicks by an average of 40 percent. The source of this problem is incorrectly counting page views — from users browsing through an advertiser's site — as clicks," (via Marketing Pilgrim).

Ghosemajumder added that the firm incorrectly counts visits to PPC ad landing pages. Click Forensics assumes "each visit to that URL corresponds to a unique click, and vice versa. But in practice this is not the case. Once a user visits a page, they typically browse through the site, navigating through sub pages, and then return to the landing page by hitting the back button."

When the landing pages is reloaded, Ghosemajumder says, Click Forensics registers it as an additional (fraudulent) click - whereas Google does not. Therefore, "the reports we receive from them ask for refunds for clicks which do not even exist" as far as Google is concerned - because Google never charged for them in the first place.