Know what’s on your site before a plaintiff’s firm does
A free privacy audit shows which cookies, pixels and trackers are running — and which ones commonly appear in privacy claims.
Advertisers who run campaigns on Microsoft Advertising (Bing, Microsoft Start and partner sites) install a Universal Event Tracking, or UET, tag to measure conversions. That tag sets _uetsid, a short-lived first-party cookie that ties together what a visitor does during one session.
What Is the _uetsid Cookie?
Microsoft’s UET FAQ says _uetsid “contains the session ID for a unique session on the site.” Microsoft notes that, as of July 2023, the cookie also carries extra values: an insights session ID, a timestamp, a page number and upgrade and upload flags.
UET uses the session ID to connect page views and events, such as a form submit or a purchase, to the same visit, so Microsoft can report conversions back to the ad campaign that drove them.
How Long Does _uetsid Last?
Commonly one day. Microsoft’s FAQ doesn’t list a lifetime, but one day is what cookie scans and Microsoft-hosted cookie tables show. Its long-term partner, _uetvid, lasts about 13 months.
Related Microsoft Cookies
_uetvid: a persistent, pseudonymous visitor ID stored on your domain._uetmsclkid: stores the Microsoft Click ID (msclkid) from an ad click, for attribution.- MUID: a Microsoft cookie on Microsoft domains with a browser GUID.
_uetmsdns: Microsoft says advertisers can set this to 1 to stop UET sending events for visitors who restrict data sharing.
If you also use Microsoft Clarity, you’ll see cookies such as _clck and ANONCHK as well.
What Data Does UET Collect?
According to Microsoft, UET can collect page URL, referrer, page title, screen size, interactions such as clicks and scrolls, time spent, page performance, and, if enabled, cart data like product names and prices. Microsoft says it uses some of this for fraud detection and audience targeting, and that it doesn’t resell the data to third parties.
Does _uetsid Need Consent?
EU, EEA and UK
Yes. It’s an advertising measurement cookie, not strictly necessary. Microsoft supports a consent mode for UET: set ad_storage to “denied” by default and update it when the visitor consents. Microsoft also says you can stop UET from setting first-party cookies with the storeConvTrackCookies:false parameter.
US states
Remarketing and cross-context ad measurement typically count as “sharing” under the CCPA. Disclose UET, honor opt-outs and Global Privacy Control, and use _uetmsdns or block the tag for opted-out visitors. Our CPRA cookie consent guide explains the California rules.
How to Block or Delete _uetsid
- Site owners: load UET through your tag manager with consent conditions, or implement Microsoft’s consent mode.
- Check Google tags too: many sites run Microsoft and Google conversion tags side by side, and Google’s _gcl_au needs the same gating.
- Visitors: clear site cookies or use a tracker blocker. The cookie expires after about a day.
Finding UET on Your Site
UET is often added by a marketing agency and forgotten. Our cookie checker guide shows how to spot it. Captain Compliance’s cookie scanner flags _uetsid and _uetvid as advertising, and our consent banner can hold the UET tag until visitors opt in.
FAQ
Is _uetsid a Bing cookie?
It’s set by Microsoft Advertising’s UET tag, which powers ads on Bing and Microsoft’s network. It’s written on your domain, not bing.com.
Does _uetsid identify me personally?
It’s a pseudonymous session ID. It doesn’t contain your name, but it’s personal data under the GDPR.
Can I use UET without cookies?
Microsoft says yes, by setting storeConvTrackCookies:false, though conversion tracking will be less accurate.
A one-day session cookie looks minor in a scan. It also means a Microsoft ad tag is running on the site, and that tag usually gets less review than Google’s or Meta’s.
Put this into practice
Turn privacy guidance into working controls.
Captain Compliance helps teams discover tracking technologies, enforce consent, manage privacy requests and document the evidence behind every decision.
