i just found an interesting article and wanted to share with dp members: http://www.marketingpilgrim.com/2006/12/google-click-fraud-rate-two-percent.html so Google say that Click Fraud Rate is Less than 2%, what do u think everybody?
I think the difference, in part, stems from definitions. What google might differentiate as invalid/inadvertant/fraud/etc, an advertiser might simply lump into fraud. I'd say its about 20% or more, depending on what your niche is. I'd suspect, the more competitive (higher the bids) the higher the fraud will be.