What is the MUID cookie?
Assigns a unique identifier to the user's browser to track interactions across Microsoft properties and client websites for advertising, analytics, and operational purposes.
Table of Contents
About MUID
| Vendor | Microsoft |
|---|---|
| Cookie Domain | bing.com,clarity.ms,forms.cloud.microsoft,microsoft.com,msn.com,office.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 28.4% of scanned pages |
| Expiration Type | Timestamp |
| Expiration Duration | 24 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 | Medium |
| Vendor Privacy Policy | https://privacy.microsoft.com/en-us/privacystatement |
| Vendor Website | https://www.microsoft.com |
What is the purpose of MUID?
The MUID cookie is a third-party tracking cookie set by Microsoft when a user visits a website that utilizes Microsoft services, such as Microsoft Advertising (via the Universal Event Tracking or UET tag), Microsoft Clarity, or Dynamics 365 Customer Voice. Its primary function is to store a Globally Unique Identifier (GUID) that uniquely identifies a web browser across different Microsoft-affiliated sites and services.
By synchronizing this identifier across domains, Microsoft uses the MUID cookie to measure advertising performance, track user conversions after ad clicks, generate aggregated behavioral analytics (such as session recordings in Microsoft Clarity), and personalize advertisements. It serves as a foundational component for cross-site tracking and attribution within the Microsoft Advertising and analytics ecosystems.
What are the Privacy Risks of MUID?
Risk Level: Medium
The MUID cookie is assigned a Medium risk level because it stores a pseudonymous, globally unique identifier (GUID) used to track users across different websites. While it does not inherently contain direct personal information like a name or email address, the identifier allows Microsoft to profile user behavior, stitch together cross-site browsing history, and measure the effectiveness of targeted advertising. This level of cross-domain behavioral tracking is considered a moderate privacy risk as it builds a detailed profile of an individual's online activities.
How to Remove MUID from a Website
To remove the MUID cookie, website administrators must locate and remove any Microsoft Advertising Universal Event Tracking (UET) tags, Microsoft Clarity scripts, or Dynamics 365 Customer Voice integrations from their website's source code and tag management systems. If the organization relies on UET for conversion tracking but wishes to prevent the tag from setting first-party variants of tracking cookies, they can modify the UET tracking code configuration by setting the storeConvTrackCookies parameter to false. However, since MUID is fundamentally a third-party tracking cookie served directly from Microsoft domains (such as bing.com or clarity.ms), entirely eliminating its presence requires fully uninstalling the associated Microsoft services from the site.