What is the KADUSERCOOKIE cookie?
KADUSERCOOKIE is set by PubMatic, one of the major global programmatic advertising technology providers, used by publishers to sell ad inventory to advertisers through real-time bidding (RTB) auctions.
The cookie appears on the .pubmatic.com domain, meaning it is set by PubMatic as a third party, typically when a page runs an ad module, ad tag, or a header bidding wrapper that includes PubMatic among its bidding partners.
What data it stores
The cookie generally stores an anonymous unique identifier generated by PubMatic to recognize the browser on subsequent visits, either on the same site or on other sites where PubMatic auctions ad space.
The exact value format is not publicly documented in detail and may vary; the information is sent to PubMatic's servers (the pubmatic.com domain) and may be shared, through cookie-syncing mechanisms, with other partners in the programmatic advertising chain.
What it is used for
For PubMatic, the cookie helps identify a user/browser during the ad auction process, build audience segments, and measure ad campaign performance.
For the site owner, this cookie is part of monetizing ad inventory through SSP/header bidding partners; it does not provide a function visible to the user directly, but it supports the delivery of potentially more relevant ads and the site's advertising revenue.
Does it require consent?
KADUSERCOOKIE falls under the marketing/advertising category and involves tracking user behavior for advertising purposes, potentially including cross-site profiling.
- Under the ePrivacy Directive (as implemented locally, e.g. Romania's Law 506/2004) and GDPR, this type of cookie requires the user's prior consent, obtained through a consent banner, before the PubMatic script executes.
- Site owners must disclose this cookie (or the marketing cookie category it belongs to) in their cookie policy and must allow consent to be withdrawn as easily as it was given.
How to block or delete KADUSERCOOKIE
A visitor can delete or block this cookie via browser settings (managing cookies per site or per third-party domain) or by using ad-tracker blocking extensions; some browsers block third-party cookies such as those from .pubmatic.com by default.
For site administrators, the cookie should be blocked automatically until consent is given, not merely disclosed in a policy. A CMP such as CookieFix can block advertising scripts that set PubMatic cookies until the visitor explicitly accepts the marketing category, reducing compliance risk.
Frequently asked questions
It is a marketing cookie set by PubMatic, used to identify a browser during programmatic ad auctions on partner websites.
No, it is a standard advertising cookie used by an SSP platform; it contains no harmful code, but it does involve tracking for marketing purposes.
Yes, as a marketing/tracking cookie, it requires prior consent under GDPR and the local ePrivacy law, obtained via a cookie consent banner.
The typically reported duration is around 3 months, after which the cookie expires automatically unless reset by a new visit.