In a latest post on Google Policy blog, Google provide some metrics that give greater insight into the scale of the problem to make ads safer by detecting and removing scam ads. David W. Baker, Director of Engineering, Advertising, writes, "Bad ads have a disproportionately negative effect on our users; even a single bad ad slipping through our defenses is one too many."
He stated, "Ads that are in violation of our ads policies aren't allowed to be shown on Google and our AdSense partner sites. For many repeat offenders, we ban not just ads but also advertisers who seek to abuse our advertising system to take advantage of people. In the case of ads that are promoting counterfeit goods, we typically ban the advertiser after only one violation."
"We're constantly working to improve our systems and utilize new techniques to prevent bad ads from appearing on Google and our partner sites. In fact, billions of ads are submitted every year for a wide variety of products. We have a set of ads policies that cover a huge array of areas in more than 40 different languages. For example, because we aim to show safe, truthful and accurate ads to our users, we don't allow ads for misleading claims, ad spam or malware," he said.
Adding, "One method we use to test the success of our efforts is to ask human raters to tell us how we're doing. These human raters review a set of sites that're advertised on Google. By using human raters, we can calibrate our automated systems and ensure that we're improving our efforts over time. In 2011, we reduced the percentage of bad ads by more than 50 percent compared with 2010. That means the proportion of bad ads that are showing on Google was halved in just a year," explains Baker.
Here are some metrics: