After catching 25 ad exchanges misrepresenting access to its inventory in September, the business news publisher took its fraud-fighting test a step further by purchasing counterfeit inventory that purported to be the FT’s to see which vendors were still selling fake FT impressions. Over few days at the end of October, the FT spent $500 on inventory that claimed to be FT.com.

The publisher found that 24 of the 25 exchanges had stopped spoofing the FT’s domain since the publisher called out the tech vendors that were selling the mislabeled inventory, said Jessica Barrett, global head of programmatic at the Financial Times. She wouldn’t say which vendor continues to misrepresent access to FT inventory.

“I was pleasantly surprised by how many exchanges were willing to work with us to fix this issue,” Barrett said, addressing the Digiday Programmatic Media Summit in New Orleans. “It was much less worse than I originally anticipated.”

In September, the FT ran a test to see which exchanges claimed to have access to its inventory and found that 10 display exchanges and 15 video exchanges falsely claimed to sell its video inventory. The FT estimated the value of the fraudulent inventory to be $1.3 million a month. The publisher demanded that several ad tech vendors, including Oath, SpotX and FreeWheel, stop representing access to its inventory.

Domain spoofing — where unscrupulous publishers and vendors obscure the nature of their traffic to resemble legitimate websites — most obviously hurts ad buyers since it leads them to waste money on junk. It also hurts publishers. The FT’s concern is that fraudulent impressions won’t drive results for advertisers, and if advertisers mistakenly think they’re getting FT inventory, they’ll blame the FT for getting a low return on investment.

The ad industry’s push for transparency likely nudged the vendors to clean up their act once the FT surfaced the amount of domain spoofing occurring in their platforms, Barrett said. With initiatives like the IAB Tech Lab protocol ads.txt — a text file that publishers host on their web servers that lists all the companies authorized to sell their inventory — taking off, vendors have incentive to hop on the clean inventory bandwagon to avoid becoming a pariah.

But just because the vast majority of exchanges stopped selling fake FT impressions once the publisher brought it to their attention doesn’t mean masked URLs claiming to be the FT won’t resurface again on their platforms.

“It’s easy to spot domain spoofing, but it is hard to put the kibosh on it,” Barrett said.