Ad Laundering: How Websites Deceive Advertisers into Rendering Ads Next to Illicit Content

Providing online content monetized via ads to users is a lucrative business. But what if the content is pirated or illicit, thus harming the brand safety of the advertiser? In this paper, we are the first to investigate Ad Laundering: a technique with which bad actors deceive advertisers by hiding illicit content within evidently lawful websites to monetize the generated traffic. We develop a client-side detection methodology to detect and analyze websites performing ad laundering. We describe in detail the techniques these websites use to cloak content, and provide estimations for the ad revenues they are able to collect on a monthly basis. Finally, we attribute the generated revenue to different traffic channels and establish that even popular brands have their ads rendered next to undesirable content.