A supply-side-platform executive, who requested anonymity to discuss sensitive industry relations, became aware of ID bridging six months ago when he observed some alternative identifiers generating a 50% match rate to third-party cookies on Safari.

How to bridge IDs

In theory, ID bridging gets buyers all the information they’d have about audiences on Chrome, like their browsing history, even though these users are on the web in other browsers and environments. A solution using ID bridging does this by trying to find an IP address, email address or other signal to match the Safari user, for example, with the cookie associated with their identity, O’Sullivan said.

But the signal or mechanism by which this bridging is happening is not always clear to the buyer, he added.

“How did you determine that there is an association between this Safari request and this Chrome-based ID?” O’Sullivan said. “A lot of time they’re relying on IP address and traditional fingerprinting signals.”

Counterproductive

While this technique will no longer be viable once cookies are deprecated, even today, it is of limited use for important use cases of advertising outside of targeting, like measurement, Roche said.

If a Safari user—identified by ID bridging—is targeted by an ad, it’s hard for the advertiser to know if that person purchased through the brand’s website, because there would be no cookie in this environment to identify them.

The behavior itself isn’t bad or good, it should just be disclosed.

Michael O’Sullivan, co-founder of Sincera

“It helps monetize impressions, but you can’t track campaign performance,” Roche said. ‘It’s counterproductive from a campaign optimization standpoint.”

For now, these solutions can be useful for monetizing audiences on Safari, Firefox and iPhone, and the technique is used by demand-side platforms today for targeting users in these environments, said a programmatic buyer.

The trouble comes when buyers and publishers are not fully aware that their cookieless solution is using this tactic, and don’t know the solution will fall apart when cookies go away.  

“The behavior itself isn’t bad or good, it should just be disclosed,” O’Sullivan said. “There are a bunch of companies that use this, but they have agreements and arrangements with buyers and publishers. It’s bad when it’s bridged and no knows about it.”