Google came out and finally gave us some numbers.
0.02 Percent of Clicks Pass Through Google's Fraud Detector:
Our Click Quality team investigates every inquiry we receive from advertisers who believe they may have been affected by undetected click fraud. Many of these cases are misunderstandings, but in most cases where malicious activity is found, the clicks have already been filtered out (and not charged for) by our real-time filters. Because of the broad operation of our proactive detection, the relatively rare cases we find of advertisers being affected by undetected click fraud constitute less than 0.02% of all clicks.
Invalid Clicks Account For Less Than 10% Of All Clicks:
Our invalid clicks rate – the activity rate – has remained in the range of less than 10% of all clicks every quarter since we launched AdWords in 2002. At Google’s current revenue rate, every percentage point of invalid clicks we throw out represents over $100 million/year in potential revenue foregone.
So, in a sense, click fraud is costing the industry $1,000,000,000 ($1 billion) per year.
totally misleading. How many advertisers can analyze (or choose to) the data and take the issue up to google?
Those 10% invalid clicks are identified as such by Google and are not charged to advertisers. What they are saying is that maybe 0.02% of those clicks are invalid *and* charged to advertisers. That sounds like peanuts and as long as advertisers have a decent ROI, I don't see what's the big deal, as long as Google is diligent with banning fraudsters. No advertising medium is 100% efficient.