When it comes to ad fraud, we hear so much about bots causing fraudulent impressions. However, several other techniques like pixel stuffing and ad stacking are not as well known.

What are they?

Pixel stuffing works by cramming advertisements of standard dimensions into tiny spaces. These spaces can be as small as 1x1 pixels, making them virtually undetectable. Several of these advertisements can be stuffed into one webpage.

Ad stacking works by layering multiple advertisements on each other. Only the cover ad is visible, while multiple hidden ads are present below it.‍

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How do they work?‍

Pixel stuffing and ad stacking are impression-based frauds.

In pixel stuffing, the crammed ads are not visible to the user, but just by visiting the infected site, an impression is registered and reported as a real view. Frauds use this technique to trigger impressions from a much higher number of ads, then there is room for on a publisher’s website.

In ad stacking, only the ad on top is visible. If the user clicks on it, all the ads in the stack register a click. If there are ten ads in a stack, one real impression can lead to nine false impressions.‍

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Impact of pixel stuffing and ad stacking‍

The most detrimental effect of pixel stuffing is that there is no limit to the number of ads crammed into one page. The higher number of registered impressions can falsely convince an advertiser of a successful campaign, while the actual truth is, they end up paying for advertisements that are never seen.

Ad stacking also has the same effect on advertising campaigns. With this one technique, scammers can employ different types of fraud like click stuffing, impression stuffing and viewability fraud.‍

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How can you be protected?‍

The one-stop solution to pixel stuffing, ad stacking and all other types of impression-based fraud is to invest in proper ad fraud technology that can detect such fraud based on suspicious activity. On detection, the infected ads can be reported and taken down. More in-house preventative action can be taken by avoiding “click-per-impression” campaigns and always being wary of KPIs and metrics. Any sudden rise should be thoroughly checked for fraudulent activity and immediately actioned against.