Depending on whom you ask, click fraud is either an unsolvable quagmire threatening the online ad industry or, as Google Chief Executive Eric Schmidt said last year, “immaterial.”That disconnect is growing. According to a July report from the click-fraud auditing firm Click Forensics, as much as 15.8% of ad clicks are fraudulent, up a full percent in just three months, the company says. On content networks like Google’s Adsense Network, Click Forensics estimates click fraud at greater than 25%, compared with less than 22% in the quarter before.Google’s click fraud czar, Shuman Ghosemajumder, disagrees. By his count, less than 10% of clicks are “invalid.” He contends that Google catches 98.8% of click fraud before charging advertisers. Last week, he responded to Click Forensics’ report, arguing that click-fraud auditing firms inflate their numbers through a mixture of shoddy methodology and inadequate information.Tom Cuthbert, Click Forensic’s chief executive, stands by his data. He spoke with Forbes.com about Google’s attempts to dismiss his company’s claims, why third parties may have a better angle on click fraud than Google itself, and the search giant’s nagging troubles with transparency.For the interview with Tom Cuthbert in Forbes, see www.forbes.com/technology/2007/09/21/google-click-fraud-advertising-tech-cx_ag_0921cuthbert.html