Google claims it has cut in half the number of so-called “bad ads” being displayed across its networks, thanks to a combination of new technologies and improved detection methods to stop fraudulent services being offered.

Improvements in monitoring for sensitive keywords, enhanced scanning methods and a faster response rate to flagged advertisements all helped lead to the significant increase in the removal of bad ads, Sridhar Ramaswamy, Google engineering chief, wrote in a blog post.

“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,” he wrote. “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.”

He added that Google was continuing to look for ways to improve its ability to stop fraudulent ads from being displayed, given the importance of ensuring it systems is trustworthy to its future success.

“We must remain vigilant because scammers will always try to find new ways to abuse our systems,” he said. “Given the number of searches on Google and the number of legitimate businesses who rely on this system to reach users, our work to remove bad ads must be precise and at scale.”

Although improved, Google’s advertising system, which contributed 96 percent of Google’s 2011 revenue, is far from perfect. Google was found to have profited from illegal Olympic ticket reseller ads and mortgage scam ads within the past year, in addition to being fined $500 million by U.S. Department of Justice for knowingly running ads by “rogue” Canadian pharmacies.

Last year Google revealed it had removed almost 100,000 ads from its UK site at the request of the Office of Fair Trading.

This article was originally published on V3.