Google wants you to know that it's on a rampage against bad ads—a problem that has become especially pressing as fake news sites try to cash in on clicks.

The world's biggest digital advertising company says it took down more than 1.7 billion ads that violated its policies in 2016—more than double the number of bad ads it eliminated one year ago. The company disabled more than 780 million bad ads in 2015, 524 million in 2014, 350 million in 2013, and 220 million in 2012.

Ninety percent of Google’s revenue comes from advertising—the company has good reason to want to keep its ad network clean.

“In the past year, what’s really changed is that we’ve expanded our policies so we can better protect consumers against issues like misleading ads and predatory offers," says Scott Spencer, Google’s director of product management for what the company calls "sustainable" ads. He says Google has also ramped up the technology it's using to be able to spot and disable bad ads.

Ninety percent of Google’s revenue comes from advertising—the company has good reason to want to keep its ad network clean. In 2011, Google agreed to pay $500 million to avoid Justice Department prosecution on allegations that it knowingly accepted illegal advertisements from Canadian online pharmacies for years. Last year, the podcast Reply All ran an episode in which the hosts try to track down a bad actor from a convoluted Google AdWords scam. Google knows the more aggressively it deals with these bad actors, the more it can build trust with its long-term customers, not to mention consumers surfing on Google’s turf—even if that does mean losing out on revenue from malicious ads and advertisers.

Google says more than 1,000 of its 66,000 employees work to remove ads that violate its policies. These include prohibitions on ads for illegal products (pharmaceuticals, for example); misleading ads; ads that “self-click” or otherwise try to game the system; and ads that promote and profit from malicious sites (weight-loss scams, counterfeit goods, sites that contain malware). The company says it's also removed more than 5 million payday loan ads since banning them in July.

Bad Actors, Bad Ads

Google also says it saw the rise of “tabloid cloakers” in 2016—scammy advertisers that make their ads look like headlines on a news website covering a particularly timely topic, like a government election or a trending news story. But when consumers click on those stories, they end up on sites that, say, sell dubious weight-loss products. In response, Google says it suspended 1,300 advertiser accounts—a stiffer penalty than kicking bad ads off one by one. Spencer says Google zeros in on such accounts by tracking a scammer’s traffic patterns, the content of their ads, and the web sites they link to to identify players who scam at scale.

Google's report does not break out one of the most serious issues of the moment: ads served on fake news sites. Google categorizes such content under its AdSense misrepresentative content policy, a series of prohibitions introduced in November that cover not just fake news sites, but also sites that phish for personal data and sell plagiarized term papers, among other sketchy activities. In the last two months of the year, Google says it reviewed 550 sites suspected of misrepresenting content to users, “including impersonating news organizations,” and took action against 340 of them. Google permanently kicked almost 200 publishers out of its network, the company said—though it’s unclear how many of these specifically peddled fake news. Right now, Google only pulls ads from clearly spoofed domains—say, a domain like FoxNews123.au, which poses as an official website. Otherwise, the company evaluates flagged sites individually, leading some to criticize the company for spotty enforcement.

Google, for its part, says it is important to move slowly to make sure it executes the new policy correctly. It's much easier to defend taking down ads from a site that's clearly masquerading as another, after all, and harder to prove that the details contained in an article under a fresh domain are fake. Google walks a fine line between banning fake news sites and appearing to be censoring sites with strong or disagreeable opinions.

Google thinks of bad ads not just in terms of malware, but in terms of the quality of the experience. The company tries to protect advertisers from incomplete display environments (non-viewable ads), criminal activity (such as the use of bots to drive clicks or page views), or running their ads in brand un-safe environments (such as having ads next to violent content). “Fake news is a relatively new type of brand un-safe environment, or at least one that advertisers are newly conscious of,” says Brian Wieser, a media industry analyst at Pivotal Research.“It falls under the ad quality issue rather than the bad ads issue.”

But ultimately, it’s in Google’s interest to nix all the bad ads it can find. Without bad ads, the quality of any site that includes ads served by Google improve, and advertisers—as well as consumers—keep coming back for more.

"Constant investment is required to keep up with all of the different types of bad actors,” says Spencer. “Our goal is to protect the consumer and the online advertising ecosystem, so that consumers can get access to good content in an open way." It’s a virtuous cycle for the company that it has several billion reasons to protect as stringently as possible.