Invalid traffic & fraud
Hidden ads
Hidden ads are ads that load and count as impressions but are placed where no one can see them, such as off-screen, behind other content, stacked or shrunk to tiny sizes.
An ad is only worth paying for if a person has a chance to see it. Hidden ads are served in ways that make that impossible: positioned far off the edge of the screen, set to be invisible, covered by other page elements, stacked under other ads (ad stacking), squeezed into 1x1 frames (pixel stuffing) or loaded in apps running in the background.
Some hiding is accidental, from sloppy page builds, but it is also a deliberate way to multiply impressions from the same traffic. In mobile apps, a notorious pattern is apps that keep loading ads while the screen is off or while the user is in another app. Under the MRC IVT guidelines, ads that could not be seen because of such manipulation are invalid, and deliberate concealment is SIVT.
Viewability measurement is the first line of defence, since hidden ads register as not viewable; the Open Measurement SDK brings that measurement into apps. Verification vendors also check element visibility, z-order and app foreground state. A placement with very high impressions and near-zero viewability deserves investigation.
Think of it like this
It is like a shop charging for window display space and then putting your poster in the stockroom.
An example
A wallpaper app on Android is found requesting ads every 30 seconds while the phone is locked, generating 2,000 impressions per device per day that no user could see.
Related terms
Ad stacking
Ad stacking is piling several ads on top of each other in one ad slot, so only the top ad is visible but every ad in the stack is counted and billed.
Pixel stuffing
Pixel stuffing is squeezing an ad, or a whole page of ads, into a tiny frame, often 1x1 pixel, so it counts as served but no one can see it.
Viewability
Viewability measures whether an ad actually had a chance to be seen on screen; the MRC standard is 50% of pixels in view for one second (display) or two seconds (video).
Open Measurement SDK (OM SDK)
The Open Measurement SDK (OM SDK) is an IAB Tech Lab standard toolkit that lets verification vendors measure viewability and invalid traffic inside apps and other environments through one shared integration.
SIVT (sophisticated invalid traffic)
SIVT (sophisticated invalid traffic) is invalid traffic designed to look human or legitimate, which can only be found through advanced analytics, multi-point corroboration and often human review.
Sources: MRC Invalid Traffic Detection and Filtration Guidelines Addendum (2020 update), MRC Viewable Ad Impression Measurement Guidelines, IAB Tech Lab Open Measurement SDK