What is the uuid2 cookie?
This cookie stores a unique identifier assigned by Microsoft's Xandr platform to distinguish individual browsers and devices for targeted advertising.
Table of Contents
About the uuid2 cookie
| Vendor | Microsoft |
|---|---|
| Cookie Domain | adnxs.com |
| Category Category The functional category of the technology, such as Web Analytics or Social Media. Learn more | Advertising & Paid Media |
| Consent Category Consent Category The consent category this cookie most commonly falls under across sites we scan, normalized into four standard categories. Learn more | Targeting & Advertising |
| Prevalence | Very Common |
| Popularity Popularity Popularity is calculated from our dataset of 4.5B+ cookies analyzed across hundreds of millions of web pages. Learn more | Found on 18.3% of scanned pages |
| Expiration Type | Timestamp |
| Expiration Duration | 29 days |
| Party Type Party Type Whether the cookie is first-party or third-party. Learn more | 3rd-Party |
| Risk Level Risk Level Rates how sensitive the data stored by this cookie is (High, Medium, or Low) based on data classification and distribution. Learn more | High |
| Vendor Privacy Policy | https://privacy.microsoft.com/en-us/privacystatement |
| Vendor Website | https://www.microsoft.com/ |
What is the purpose of the uuid2 cookie?
The uuid2 cookie is a third-party tracking identifier set by the Xandr programmatic advertising platform (formerly AppNexus, which was acquired by AT&T in 2018 and subsequently sold to Microsoft, with the deal announced in 2021 and completed in 2022). It stores a unique, randomly generated value that enables the platform to recognize a specific browser or device across multiple websites and sessions.
This identifier is critical for real-time bidding (RTB) and programmatic advertising. It allows Xandr to build behavioral profiles, match users against advertising interest segments, track the history of ads shown on a device (for frequency capping and performance attribution), and synchronize user identities with other third-party demand-side platforms (DSPs) and data brokers. By persisting this ID, advertisers can serve highly personalized, interest-based advertisements to users across the web.
What are the Privacy Risks of the uuid2 cookie?
Risk Level: High
The uuid2 cookie contains a persistent unique identifier that enables extensive cross-site tracking and behavioral profiling across the internet. Because it actively facilitates the synchronization of user profiles with various third-party demand-side platforms and data brokers for real-time ad bidding, it exposes visitors to significant privacy risks. Such data is widely classified as personal data or "sale/sharing of personal data" under GDPR, CCPA, and other privacy regulations.
How to Remove the uuid2 cookie from a Website
To remove this cookie, site administrators must locate and eliminate the Xandr (AppNexus) Universal Pixel, Prebid.js integration, or related ad-server tags from the website's source code or tag management system. Because this cookie is fundamental to Xandr's programmatic bidding and ad targeting capabilities, it cannot be disabled independently of the service itself. If the website relies on Xandr for monetization or campaign tracking, administrators cannot remove the cookie without suspending the programmatic advertising service.