@wchr I worked in ad tech. To say it went "undetected" is incorrect: malicious ads & fraud were ok so long as they made money & no one important enough complained. One company I worked at made in the ballpark of 40% of their income off of fraud (refreshing ads in inactive tabs), though admittedly I was hired to reduce this (people important enough had complained). I can say with confidence through that the majority of ad impressions on the Internet are fraud.