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Cookie Deception Sparks Tension Between Buy and Sell Side in IAB Tech Lab

Buy-side tech platforms are accusing publishers and the tech firms they work with of using deceptive practices to identify audiences in discussions happening within the IAB Tech Lab over the past month, ADWEEK can exclusively report.

These tactics, spurred by signal loss, can obscure digital marketing efficacy, making techniques like conversion tracking and frequency capping more difficult for marketers.

In digital advertising, demand-side platforms (DSPs) decide which audiences they want to buy on behalf of their brand clients using third-party cookies, which identify users across the web.

Other ways of identifying users have emerged as web browsers like Safari, Firefox, and soon Chrome, have deprecated third-party cookies. Sell-side platforms are using some of these techniques without the buy side knowing, the DSPs allege, according to six sources.

“This is literally an exchange applying some technology they never told anybody,” said one DSP executive, who requested anonymity to discuss sensitive industry relations. “It’s manipulating the contents of a bid request in abnormal ways whenever you feel like. It’s a really alarming precedent.”

As signal loss continues, due to browser crack-down and privacy-preserving regulation, sell-side partners are looking for ways to identify audiences to keep marketer budgets flowing. But the extent of how shady these practices are depends on the transparency between the DSP and supply-side platforms (SSPs).


These allegedly clandestine targeting mechanisms often take the form of probabilistic identifiers, which use machine learning to guess who a reader of a website might be. This includes ID bridging, a technique where an ad-tech firm approximates who a user might be in a cookieless environment like Safari by linking the user to their identity on Chrome. And because the buy side does not know the exact method the sell side is using instead of cookies, some equate this to outright fraud.

Sell-side platforms and publisher networks have not necessarily denied that they engage in ID bridging and other probabilistic techniques in IAB Tech Lab conversations. But some reject that these practices are being done deceptively, arguing DSPs have ways of knowing what’s going on, two sources said.

This smells to me as a desperate way to recover some of that revenue.

—Anonymous DSP exec

These techniques in question are often used in cookieless environments and became more apparent in early February, a month after Google Chrome deprecated cookies for 1% of web traffic, which is when the conversations in the IAB Tech Lab began.

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