Last month, Guardian US and programmatic partner MightyHive teamed up with Google to test how much ad inventory being sold on the open marketplace was not legit.

The team purchased ad inventory—ostensibly from Guardian US—through demand-side platform (DSP) buying via the open marketplace. A similar buy was made specifying verification from ads.txt, a program adopted by publishers to signal that their inventory is what it says it is.

What they found was clear evidence that unauthorized players were pretending to sell Guardian inventory and diverting the revenue to themselves. Of the video ad inventory purchased without validation, 72% was fraudulent.

The good news was that the buy using ads.txt verification seemed to have worked, with the Guardian seeing all the revenue from that campaign.

eMarketer’s latest report, “Cleaning Up the Digital Media Supply Chain: What Will Move the Industry Toward Transparency and Optimization?” examines the current state of the programmatic media supply chain, why advertisers are concerned and what the ecosystem is doing about it.

The top challenge of addressing ad quality issues is tracking down bad actors in the supply chain, according to January 2018 research by ad intelligence firm Ad Lightning. Nearly six in 10 of the US ad operations professionals surveyed called it a significant problem.