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Domain spoofing and ad fraud: why ads.txt exists
By the ads-txt.in team · Published November 8, 2026
Online advertising moves billions of rupees through automated auctions every day. Where money moves automatically, fraud follows. Understanding the problem helps explain why ad networks keep asking publishers to maintain an accurate ads.txt file.
How programmatic ads are sold
When someone opens a page, the publisher’s ad system sends a bid request to exchanges describing the ad space: the website, the page, the ad size and some details about the visit. Advertisers’ platforms decide in a fraction of a second whether to bid. The highest bid wins and its ad appears.
What domain spoofing is
Bid requests describe the website, but in the early days nothing proved that description was true. A fraudster could send requests claiming to come from a famous news site while actually showing ads on a low-quality site, or to bots that never involved a real person. Advertisers paid premium prices for worthless impressions, and the real news site lost money it never knew about.
How ads.txt stops it
ads.txt gives every publisher a simple way to say publicly: “These are the only accounts allowed to sell my ad space.” Because the file sits on the publisher’s own domain, only the site owner can change it. A buyer receiving a bid request for example.com can check example.com/ads.txt. If the seller’s account is not listed, the buyer can refuse to bid. Spoofers cannot add themselves to a file they do not control.
Closing the remaining gaps
ads.txt answers “who may sell this site’s ads?” Two later standards complete the picture. sellers.json, published by ad systems, lists the companies behind each account ID, so buyers can see who they are dealing with. SupplyChain object data travels with each bid request and records every company that handled it. Together they let buyers trace a purchase from the advertiser to the publisher. For mobile apps, app-ads.txt does the same job.
What this means for you
- Keep your ads.txt file up to date. Remove lines for networks you no longer use, so nobody can misuse old accounts.
- Only add lines from partners you actually work with.
- Check the file after website migrations or theme changes, which sometimes delete it.
A correct file protects advertisers, and in turn protects your income, because buyers spend more confidently on inventory they can verify. You can check yours with our ads.txt checker.