Pixel stuffing

An ad needs space to be seen. Pixel stuffing cheats by loading ads, or a whole ad-filled page, inside a microscopic frame hidden on another page. Every ad inside fires its impression tracking, so the advertiser pays, yet the whole thing is smaller than a full stop.

It is often used to monetise junk traffic: a visitor to one site unknowingly loads dozens of ads from a second, hidden page. Because the inner page's ad calls can carry that page's own domain, it can also help launder traffic. It sits alongside ad stacking as a form of hidden ads and is treated as invalid traffic.

Detection is fairly direct: verification tags measure the actual size and position of the ad container, and viewability measurement will record the ad as not viewable. Buyers who pay only for viewable impressions are better protected, although fraudsters also try to falsify viewability signals, which is itself SIVT.

Think of it like this

It is like printing a full newspaper advert at the size of a grain of rice and still charging the full-page rate.

An example

A verification vendor measuring a campaign in Spain finds 180,000 impressions rendered in 1x1 iframes on a single domain; all show 0% viewability and are excluded from billing.