What is the _uetsid cookie?
_uetsid is stored by the UET (Universal Event Tracking) tag from Microsoft Advertising, the ad platform behind campaigns on Bing, Microsoft News, Outlook.com, and the Microsoft partner network. The cookie appears on a site as soon as the UET tracking code loads on a page, regardless of whether the visitor arrived from a paid ad or not.
It is used by marketers, online stores, and any site running Microsoft Advertising campaigns to connect on-site visits to the advertising source of the traffic.
What data it stores
_uetsid stores a randomly generated identifier unique to the current browsing session, along with a timestamp used for expiration. The value typically does not contain directly identifiable information (name, email), but it is still considered personal data because it allows a visitor to be recognized throughout a session and their actions to be linked together.
Data collected through this cookie (pages visited, conversion events) is sent to Microsoft Advertising's servers and may be combined with other tracking signals (such as _uetvid) for reporting and retargeting purposes.
What it is used for
The main purpose is measuring the performance of Microsoft Advertising campaigns: how many ad-driven sessions resulted in a conversion (order, form submission, call). Besides conversion attribution, the cookie underpins retargeting features and automated bid optimization within Microsoft Advertising, helping the site show more relevant ads to users who have already visited it.
Does it require consent?
_uetsid is classified as a marketing (advertising/tracking) cookie and is not strictly necessary for the website to function. Under the ePrivacy Directive (as implemented in Romania through Law 506/2004) and the GDPR, placing it requires the visitor's prior, freely given and informed consent, obtained before the UET script loads.
- Site owners must disclose this cookie in their cookie policy, including its purpose and duration.
- Consent must be as easy to withdraw as it was to give.
- Supervisory authorities (in Romania, ANSPDCP) can sanction the use of marketing cookies without valid consent.
How to block or delete _uetsid
Visitors can delete or block _uetsid from their browser's privacy/cookie settings (Chrome, Firefox, Edge, Safari) or via ad-tracking blocker extensions. Since it's a session cookie, it expires anyway after roughly 1 day of inactivity.
For site owners, the safer approach is not to rely on manual deletion but to use a Consent Management Platform such as CookieFix, which automatically blocks the UET script until the visitor gives explicit consent for the marketing category.
Frequently asked questions
No, it doesn't contain malware and doesn't access sensitive data; it's used solely for advertising measurement. It is still a tracking tool that raises privacy concerns, which is why consent is required.
_uetsid identifies a single browsing session and expires after about 1 day, while _uetvid identifies the visitor over a longer period, across multiple sessions and visits.
Yes. As a marketing/tracking cookie, it requires the visitor's prior consent under the ePrivacy rules and GDPR before it is set.
The cookie appears whenever the site has the Microsoft Advertising UET script installed, usually to measure conversions from Bing/Microsoft Ads campaigns, even if the current visitor didn't arrive via an ad.