Identity: cookies, IDs and clean rooms
How advertisers recognise the same person across sites, and what replaces third-party cookies when they are not available.
Identity: cookies, IDs and clean rooms
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You visit two sites
You browse a shoe store, then read the news. Each site, and the ad tech on it, gives your browser its own ID in a cookie.
- You visit two sites: You browse a shoe store, then read the news. Each site, and the ad tech on it, gives your browser its own ID in a cookie.
- Different IDs for the same person: Cookie A and cookie B do not know they are the same browser. On their own, the shoe ad cannot follow you to the news site.
- Cookie syncing joins them: Third-party cookies and cookie syncing let ad platforms swap IDs in the background, so A and B are matched. That is how retargeting works across the web.
- Where cookies fail: Safari and Firefox restrict third-party cookies, and apps never had them. Chrome still allows them (Google dropped its plan to remove them), but many people still cannot be matched this way.
- Logged-in IDs: When you log in, your email can be turned into a one-way hashed ID such as UID2. It is stable across sites that use it, and you can opt out.
- Clean rooms: match without handing over data: In a data clean room, a retailer and a brand match their customer lists in a controlled space and only see aggregated results, never each other’s raw data.
Step by step
- You visit two sitesYou browse a shoe store, then read the news. Each site, and the ad tech on it, gives your browser its own ID in a cookie.
- Different IDs for the same personCookie A and cookie B do not know they are the same browser. On their own, the shoe ad cannot follow you to the news site.
- Cookie syncing joins themThird-party cookies and cookie syncing let ad platforms swap IDs in the background, so A and B are matched. That is how retargeting works across the web.
- Where cookies failSafari and Firefox restrict third-party cookies, and apps never had them. Chrome still allows them (Google dropped its plan to remove them), but many people still cannot be matched this way.
- Logged-in IDsWhen you log in, your email can be turned into a one-way hashed ID such as UID2. It is stable across sites that use it, and you can opt out.
- Clean rooms: match without handing over dataIn a data clean room, a retailer and a brand match their customer lists in a controlled space and only see aggregated results, never each other’s raw data.