What is the uid cookie?
"uid" is an HTTP cookie used by Criteo, one of the largest advertising retargeting providers in Europe. It appears on a website when that site integrates a Criteo tag or pixel, typically through an online store or affiliate platform running remarketing campaigns via Criteo.
The cookie is set on the .criteo.com domain (a third-party cookie from the visited site's perspective), not by the website itself. It is read by Criteo across multiple partner sites to build a behavioral profile of the user.
What data it stores
The "uid" cookie stores a unique, randomly generated identifier assigned to the visitor's browser. The exact value format is not publicly documented in detail and may vary; it typically does not contain directly identifiable data such as a name or email address, but it functions as a persistent device/browser identifier.
The data associated with this identifier (pages visited, products viewed, ad interactions) is sent to Criteo's servers and may be matched with information collected from other sites in the Criteo partner network.
What it is used for
The main purpose is retargeting advertising: Criteo uses this identifier to recognize a visitor who previously interacted with a site (for example, viewed a product without purchasing) and later show them personalized ads on other sites within the Criteo network.
For the website owner, this cookie enables remarketing campaigns through Criteo aimed at recovering visitors who did not complete an action (such as a purchase) and improving conversion rates.
Does it require consent?
"uid" falls under the marketing/advertising category. Under the ePrivacy Directive (as transposed in Romania by Law 506/2004) and GDPR, this type of cookie requires the user's prior, explicit consent before being set, since it is used for cross-site tracking and behavioral profiling.
- The site owner must disclose this cookie in the cookie policy, including provider, purpose, and duration.
- The Criteo script must only load after consent for the marketing category has been obtained.
- Rejecting consent must be as easy as accepting it, and users must be able to withdraw consent at any time.
How to block or delete uid
A visitor can manually delete or block the "uid" cookie from browser settings (Chrome, Firefox, Edge, Safari) under cookie management for the criteo.com domain, or enable options that block third-party/tracking cookies. Criteo also provides its own opt-out mechanism through platforms like Your Online Choices / NAI.
From the site owner's side, the most effective approach is to automatically block the Criteo script until consent is given, using a CMP such as CookieFix, which blocks marketing scripts by default and only activates them after the visitor accepts the relevant category.
Frequently asked questions
It is a unique identifier set by Criteo on the .criteo.com domain, used to recognize a browser for advertising retargeting purposes.
It typically doesn't contain directly identifiable data, but it enables tracking browsing behavior across multiple sites, which is why it's classified as marketing/tracking.
The typical duration is around 13 months from the last interaction, but it can be renewed with each visit.
Yes, since it is a marketing cookie used for profiling and targeted advertising, it requires the user's prior consent under GDPR and ePrivacy rules.