Look at it this way, click fraudsters are parasitic to advertisers but actually symbiotic for web sites and ad networks. So how can you expect them to aggressiv

Look at it this way, click fraudsters are parasitic to advertisers but actually symbiotic for web sites and ad networks. So how can you expect them to aggressively prevent it? As long as the fraud doesn't rise to the point where the advertisers can't make money, they'll continue to run ads because the process is opaque and there aren't a lot of other viable choices.