Google Click Fraud ISN'T 0.02%

Deliberately confusing perhaps, the 0.02% figure is the number of clicks investigated by Google (at the behest of an AdWords customer) and found to fraudulent, as a percentage of all clicks in the entire AdWords system.

The vast majority of AdWords customers would never suspect click fraud or contact Google about it. The only real way to discover the click fraud rate would be for Google to take 100,000 random "valid" clicks from their system and check them one by one. My guess is that 2% might be more accurate. More here