Strategy very similar to that of the entertainment industry fighting piracy
With billions of ads submitted to Google every year, we use a combination of sophisticated technology and manual review to detect and remove these sorts of ads. We spend millions of dollars building technical architecture and advanced machine learning models to fight this battle. These systems are designed to detect and remove ads for malicious download sites that contain malware or a virus before these ads could appear on Google. Our automated systems also scan and review landing pages—the websites that people are taken to once they click—as well as advertiser accounts. When potentially objectionable ads are flagged by our automated systems, our policy specialists review the ads, sites and accounts in detail and take action.
The numbers show we’re having success. In 2011, advertisers submitted billions of ads to Google, and of those, we disabled more than 130 million ads. And our systems continue to improve—in fact, in 2011 we reduced the percentage of bad ads by more than 50% compared with 2010. That means that our methods are working. We’re also catching the vast majority of these scam ads before they ever appear on Google or on any of our partner networks. For example, in 2011, we shut down approximately 150,000 accounts for attempting to advertise counterfeit goods, and more than 95% of these accounts were discovered through our own detection efforts and risk models.
Google already banned 800,000 advertisers
Much more:
http://googleblog.blogspot.com/2012/03/making-our-ads-better-for-everyone.html
