What is ad stacking?
Ad stacking is a type of mobile display fraud in which an ad network or publisher layers or “stacks” multiple ads in one ad placement unit. Only the top ad is visible but clicks or impressions are registered — and billed — for the other ads in the stack, even though they weren’t visible.
How to detect ad stacking
The best way to detect whether you are subject to ad stacking is to look at conversion from impression to click/install. Campaigns impacted by ad stacking or other sorts of display fraud tend to have high impressions and low click through rates or install rates.