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 (CPM) campaigns. In a cost-per-click (CPC) campaign, ad stacking can be considered a form of click spam.

Ad stacking 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 a  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, making them invisible to the user.

Another way fraudsters implement an ad stack is to script load a static placeholder image visible to the user while a video ad is rendered in the background, continuously making ad calls that result 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 budget for marketers. Not only is there upfront budget wastage, but it skews campaign performance data, which can lead to larger-scale waste. For example, it may appear that Channel A is great for ad engagement, so a marketer moves budget from Channel B and Channel C to further boost the ads in Channel A. However, real users are not seeing or clicking these ads. The fake clicks and impressions deplete advertiser’s budgets for nothing in return, resulting in a poor return on ad spend (ROAS). This is why it’s important to take ROI into high consideration as a KPI, rather than taking impressions or engagements at face value.

Ad stacking can also lead a marketer to believe a creative is performing poorly due to the relatively low conversion rate. Unwitting publishers who are unaware that they are displaying these fraudulent ads can even be impacted from ad stacking damaging their reputation and viewability metrics.

Adjust’s Fraud Prevention Suite works specifically to combat and prevent mobile ad 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.

From Datascape, you can view your rejected installs and rejected reattributions under ‘fraud prevention’. Get a breakdown of device-level fraud and engagement fraud by date, app, country, channel, or campaign name. Adjust is widely held as the gold standard for mobile ad fraud prevention, offering solutions against fake installs, click spam, click injection, device emulators, and SDK spoofing–saving budgets and keeping your dataset clean.

To see real examples of fraud prevention in action, check out our case studies. To learn more about protecting your marketing budget by preventing fraud with Adjust, request a demo.