I'm sure this is right. You don't have enough statistical mass with any click by itself, but in the aggregate you can detect fraudulent activity with a high deg

I'm sure this is right. You don't have enough statistical mass with any click by itself, but in the aggregate you can detect fraudulent activity with a high degree of certainty. Google's plan is to make it sufficiently expensive to avoid detection in the aggregate that selling fake clicks isn't a viable business proposition. The fraudsters have inverted the game: they can't beat Google's detection algorithms, so they can't sell you fake clicks, but they can sell you protection from their fake clicks. Google's move at this point seems to be lessening the punishment for fake clicks so it's still not economically viable to sell them but also not economically viable to use them as a threat.