The Google report on third-party click fraud auditing is critical of poorly substantiated estimates of click fraud. Quote:
Over the last year, these estimates have received widespread media coverage. A different kind of report (from Outsell, Inc.) has also been widely cited for estimating the scope of the problem. But in fact that report did not measure click fraud it was an opinion survey of advertisers asking them to guess at the extent of the problem. Thus the report's conclusions about the percentage of fraud and financial loss for the industry are essentially a poll of the perception of the size of the problem (with the backdrop of the previous coverage of high estimates) rather than actual size of the problem. This is analogous to estimating crime rates in a country by asking some residents how much crime they think there is, and averaging those guesses to state that number is the actual rate.
The main problem seems to be fictitious clicks of two kinds:
- Fictitious clicks due to detection of page reloads as ad clicks.
- Fictitious clicks due to conflation across advertisers and ad networks.
In the early days of Visitlab, such clicks showed as multiple (suspicious) clicks but no more.
I have not seen the second kind of problem, where each click goes through a third party audit service and clicks within the site are counted, as are clicks arising on another advertiser service such as Overture/Yahoo.