What is ad stacking?

Ad stacking is a type of mobile ad fraud in which multiple ads are layered or ‘stacked’ on top of each other in a single ad placement. While only the top ad is visible to the user, a click or impression is registered for every ad in the stack, leading advertisers to pay for fake impressions and/or clicks.

Ad stacking is one of the most common forms of ad fraud that plagues Cost Per Mille campaigns. When ad stacking takes place during a click-based campaign, it can be considered a form of Click Spam.

Ad stacking happens exactly how it sounds, but can be executed by fraudsters in a variety of ways.

For instance, instead of serving one ad per ad unit, a fraudulent publisher script calls ads and stacks them into the single ad unit. Only one ad will be visible to the user, with dozens of other ads in the placement loaded at an opacity of zero or near-zero, rendering them invisible to the user.

In another case, a script loaded a static placeholder image visible to the user while a video ad rendered in the background, continuously making ad calls that resulted in impressions. Some fraudsters will load invisible ads on a banner rotation, meaning that behind the visible ad, a continuous invisible ad auction is happening. Once an ad has lasted long enough to be counted as an impression, another ad is loaded in its place.

These ads are never seen by the user, but since they load the required pixel to trigger an ad impression, advertisers pay for these fraudulent impressions or clicks.

Like all forms of mobile ad fraud, ad stacking results in wasted ad spend for marketers, as well as skewed campaign data. The fake impressions and clicks deplete advertiser’s budgets for nothing in return, resulting in a poor return on ad spend (ROAS). Impressions or clicks received from ad stacking also ruin campaign data, as a marketer may believe the low conversion rate relative to the amount of impressions may indicate a bad creative, when in reality the data is just untrustworthy. Ad stacking can also damage the reputation and viewability metrics of unwitting publishers unaware they are displaying these fraudulent ads.

Adjust’s Fraud Prevention Suite works specifically to combat and prevent user acquisition fraud. Ad stacking is relatively easy to catch, as it can be detected by comparing timestamps for the fraudulent impressions and clicks. The Fraud Prevention Suite is effective for combating all types of mobile ad fraud, as it analyzes each and every install event in real-time, scanning for abnormalities and potentially fraudulent action. Adjust FPS filters are widely held as the gold standard for fraud prevention, offering solutions against fake installs, click spam, and click injection, saving wasted budgets and keeping your dataset clean.

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