Ad stacking is a deceptive practice in mobile advertising where multiple ads are layered or ‘stacked’ in a single ad space. In this scenario, only the topmost ad is visible to the user. However, a click or an impression is falsely registered for every ad in the stack. This deceptive practice leads advertisers to unwittingly pay for multiple, non-genuine impressions and/or clicks, even though the user only sees one ad.
This fraudulent tactic is particularly prevalent in Cost Per Mille (CPM) campaigns, where advertisers pay per thousand impressions. Ad stacking significantly inflates impression counts, thereby defrauding advertisers. In click-based campaigns, ad stacking often overlaps with click spam, another fraudulent activity where fake clicks are generated.
Ad stacking is executed in various sophisticated ways. One common method involves a fraudulent publisher’s script that, instead of serving a single ad, stacks multiple ads into one ad unit. To the user, only one ad is visible, while many others, set to near-zero opacity, are hidden behind it.
Another method involves using a static image as a placeholder that the user sees, while in the background, a video ad plays, continuously generating ad calls and thus impressions. Some fraudsters implement a rotating banner system, where invisible ads are continuously auctioned and swapped behind a visible ad. These ads, although never seen by the user, trigger the pixel count necessary for registering an ad impression, resulting in advertisers paying for these illegitimate impressions or clicks.
Ad stacking poses significant ethical and financial challenges in the digital advertising industry. It not only leads to financial losses for advertisers but also undermines the integrity of digital advertising metrics. Detecting and mitigating ad stacking is crucial for maintaining transparency and trust in digital advertising ecosystems.