CTR is useless without hard numbers on clickfraud.<p>If every click was a 'real' click then it would go a long way towards getting an idea about conversion rates and so on on new traffic to your site.<p>With clickfraud an unknown all the numbers that depend on it are also unknowns.<p>There was a time that we spent a ton of money on adwords, it started off real well, then after a while we realized we were still paying about the same money as before, but no sales came out of the traffic that we bought.<p>There are some really tricky things going on here, one of them is that as long as advertisers don't wise up to CTR not being a very relevant metric (end-to-end conversion is) that there is very little incentive to combat click fraud, as long as it is not too blatant.<p>It directly increases the bottom line for the middlemen, and the defrauders both, at the expense of the advertisers.<p>Your tracking has to be very precise to document exactly which users are fraudulent and which ones are not. Simple checks such as seeing how 'deep' a user goes on your page, or whether or not they get style sheets and other static stuff no longer is enough to make a classification.<p>Impression based metrics are even worse.<p>The only system that comes anywhere near working is performance based advertising, but that can be very hard to couple to a large number of products.