A massive fraudulent advertising business disrupted through more than 240 apps in Google Play generated profits that could amount to more than $150,000 per day. At its peak, this operation garnered more than 15 million ad impressions per day, researchers say. The code for the OOC ads was present in packages from legitimate Android and Unity software development kits (SDKs) that had been modified by the attackers. Google promptly removed all of the rogue apps from the Android Play store after White Ops responsible reporting.
Source: https://www.bleepingcomputer.com/news/security/rainbowmix-apps-generate-150-000-in-daily-ad-fraud-profit/