Click Fraud: Less Than 2%

Straight from Google, via Andy Beal... although "invalid" and "fradulent" clicks are perhaps occuring at a rate of 9-10%, most are picked up by Google and never make it into someone's Adwords reports. Those that get through, that advertisers using appropriate click fraud monitoring could discover, are less than 2%.

I would guess that the figure not mentioned is that x% of advertisers are actually suffering higher rates - especially those whose ads show via the AdSense network, and are already paying high costs per click. I reckon perhaps 2-5% of advertisers fit into this category, and their rate of click fraud could be has high as 20%.