What is the MUID cookie?
Identifies unique web browsers visiting Microsoft sites. These cookies are used for advertising, site analytics, and other operational purposes.
Our October 2026 scan found it on 38 sites (2% of the 2,450 we scanned), set before any consent.
- Purpose
- Advertising
- Belongs to
- Bing / Microsoft
- Set as
- First-party on 8% of sites, third-party on 92%
- Typical lifetime
- 13 months (vendor says: 1 year) — about what the vendor documents
Sites that set MUID before consent
The highest-ranked 30 of 38 sites.
- bing.com0 tracking companies
- msn.com4 tracking companies
- media.net6 tracking companies
- oxylabs.io11 tracking companies
- xbox.com1 tracking company
- fidelity.com15 tracking companies
- tailscale.com7 tracking companies
- instructure.com17 tracking companies
- twilio.com9 tracking companies
- cmu.edu6 tracking companies
Show 20 more sites
- hpe.com10 tracking companies
- mgid.com9 tracking companies
- verizon.com20 tracking companies
- ford.com17 tracking companies
- crunchyroll.com4 tracking companies
- ssl.com9 tracking companies
- audible.com25 tracking companies
- redis.io12 tracking companies
- aarp.org30 tracking companies
- simplisafe.com31 tracking companies
- heylink.me7 tracking companies
- zapier.com3 tracking companies
- xero.com18 tracking companies
- guard.io14 tracking companies
- vt.edu10 tracking companies
- samsclub.com2 tracking companies
- abebooks.com3 tracking companies
- sundaysky.com16 tracking companies
- teacherspayteachers.com5 tracking companies
- wufoo.com9 tracking companies
Related cookies
Other cookies from Bing / Microsoft.
- ASP.NET_SessionId23 sites
- _uetsid22 sites
- _uetvid21 sites
- MR16 sites
- ai_session13 sites
How to stop it
Declining non-essential cookies in a site's consent banner should stop MUID being set on later visits. Blocking third-party cookies in your browser settings stops the third-party kind everywhere, and clearing cookies for a site removes any it already set.
Description from the Open Cookie Database (Apache 2.0).
Understanding this page
- How cookie lifetimes work, and why a 13-month _ga matters
What a cookie's "expires" field actually controls, why Google Analytics ships a 2-year default that many sites cut down to 13 months, and how Safari's 7-day cap on script-set cookies changes the picture.
- First-party vs third-party cookies (and why "first-party" still tracks you)
What the distinction actually means technically, why browsers only block one of the two, and how CNAME cloaking, server-side tagging and cookies like _ga let sites keep tracking under their own domain.
- How to block or limit trackers
Browser privacy settings, content blockers, Global Privacy Control and clearing cookies compared honestly — what each one actually stops, what it doesn't, and what it costs you in return.