What is the _uetsid cookie?
This cookie is set by Microsoft Advertising's Universal Event Tracking (UET) to store a unique session identifier, enabling the tracking of user interactions and conversion attribution.
Table of Contents
About the _uetsid cookie
| Vendor | Microsoft |
|---|---|
| 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 18.9% of scanned pages |
| Expiration Type | Timestamp |
| Expiration Duration | 1 day |
| Party Type Party Type Whether the cookie is first-party or third-party. Learn more | 1st-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 | Medium |
| Vendor Privacy Policy | https://privacy.microsoft.com/en-us/privacystatement |
| Vendor Website | https://ads.microsoft.com/ |
What is the purpose of the _uetsid cookie?
The _uetsid cookie is a first-party tracking cookie deployed by Microsoft Advertising's Universal Event Tracking (UET) tag (loaded from bat.bing.com/bat.js). Its primary function is to store a unique session identifier that links a visitor's actions across multiple page views during a single browsing session. This session data is transmitted back to Microsoft's tracking domains to help advertisers measure the effectiveness of their paid search campaigns, track user conversions, and build audience segments for remarketing.
The cookie value typically contains a GUID-style identifier and may include additional session metadata (such as page sequence and timing). In real-world deployments it is overwhelmingly observed as a first-party cookie with a short lifetime of about one day, refreshed on activity. Under UET Consent Mode, when advertising consent is denied the cookie may be initialized with placeholder (e.g., null|...) values that do not contain personal identifiers until consent is granted.
What are the Privacy Risks of the _uetsid cookie?
Risk Level: Medium
This cookie is classified as Medium risk because it stores a pseudonymous session identifier and captures user behavioral data (such as page views and interactions) that is transmitted to Microsoft Advertising. This information supports conversion attribution, audience building, and remarketing - i.e., behavioral profiling and cross-session tracking - but the cookie itself is an anonymized session ID rather than a direct carrier of personally identifiable information, which keeps it below the High threshold.
How to Remove the _uetsid cookie from a Website
The _uetsid cookie is set automatically by the Microsoft Advertising Universal Event Tracking (UET) tag and is integral to UET's session/conversion tracking - it cannot be selectively disabled while the tag remains active, as there is no documented per-cookie opt-out for it. To stop this cookie from being set, the website administrator must remove the UET tag (bat.js / the UET tag ID) from the site's source code or from the tag management system (e.g., Google Tag Manager) that injects it. If conversion tracking is still required, removing only this cookie is not supported; the cookie is written whenever the UET tag runs and writes first-party cookies. (Note: Microsoft's UET ad_storage consent-mode signal can prevent the cookie from being written for users who have not consented, but gating via consent is a compliance control, not removal of the cookie from the deployment.)