Another common scam came with this summer's Ebola outbreak. When the first US cases of the disease were reported, search traffic for "ebola" went through the roof, attracting scammers. Shortly afterwards, the first phony ebola treatments surfaced,selling discredited treatments for the disease. Since AdWords has a blanket policy against misleading claims, the ads were easy to weed out once identified.
Because of the immense scale involved, bad ads are typically flagged through algorithms and then investigated in-person. Google has a number of quirkily named tools designed specifically for that purpose — the index of ads is known as Beaker, while the analytics tool is called Bunsen — but the key moment in each case is noticing something's not right. "Once we have a lead on where we think there's going to be problems, we can use those tools to operate on a lot of different kinds of badness," said Ads Engineering director Vikaram Gupta.