Fraud is diverting a large portion of digital ad spending to criminal groups. There are hundreds or thousands of times more fake websites and apps than legitimate ones, and these fake sites sell ad space at low prices, diverting billions annually from publishers and advertisers. New botnets and malware strains have emerged that can generate billions of fraudulent ad impressions per minute by simulating human behavior. As a result, as much as half of all digital ad spending may be lost to fraud.