tl;dr: A developer running Google Ads for his puzzle app Dayzle found that 33 of 56 billed installs came from a likely bot farm: devices installing an old, no-longer-served APK, opening the app once, and vanishing. The farm exploited Google's install-based conversion optimization, creating a feedback loop that funneled more ad spend to the bots. His fix: change the campaign goal from "app opened" to "won a puzzle," making his app costlier to fake than to farm.