What is the mc cookie?
„mc” is an HTTP cookie set by Quantcast, a company specializing in audience measurement and digital advertising, part of Quantcast International Limited. It appears on a website when that site integrates the Quantcast Measure script or participates in Quantcast's programmatic advertising platform, either directly or through third-party ad partners.
The cookie is placed on the .quantserve.com domain, making it a third-party cookie from the perspective of the site being visited, even though it appears as a result of a script embedded on that page.
What data it stores
The „mc” cookie stores a unique identifier associated with the visitor's browser, used by Quantcast to recognize that browser on subsequent visits, both on the same site and across other sites in the Quantcast network. The exact value format is not publicly documented in detail and may vary.
Data collected through this identifier (pages visited, browsing behavior, matching to audience segments) is sent to Quantcast's servers, which may use it for audience reporting and real-time bidding (RTB) advertising auctions, including with third-party partners in the programmatic advertising chain.
What it is used for
- Recognizing unique browsers for visitor counting and browsing behavior measurement (Quantcast Measure)
- Building audience segments for targeted advertising
- Participating in real-time bidding (RTB) auctions with partners in the Quantcast ecosystem
- Providing audience reports to site owners or Quantcast's advertising clients
Does it require consent?
In CookieFix's classification, „mc” falls under the marketing category (advertising/tracking). Under GDPR and the ePrivacy Directive, this type of cookie is not strictly necessary for the site to function, so it requires prior, explicit visitor consent before being set.
Site owners must disclose this cookie in their cookie policy, include it under the marketing category in the consent banner, and make sure the Quantcast script does not load before the visitor gives consent. Failing to obtain prior consent exposes the site to potential enforcement action from data protection authorities.
How to block or delete mc
A visitor can manually delete or block the „mc” cookie from browser settings (Chrome, Firefox, Edge, Safari) under cookie management for the quantserve.com domain, or use an anti-tracking browser extension.
For site owners, the correct approach is not manual deletion but preventing the Quantcast script from loading before consent is given. A CMP such as CookieFix can automatically block the script associated with the „mc” cookie until the visitor consents to the marketing category, preventing the cookie from being set without authorization.
Frequently asked questions
It's a marketing/tracking cookie used by Quantcast to recognize a visitor's browser for audience measurement and targeted advertising purposes.
Its typical duration is 13 months from the visitor's last interaction with a site using Quantcast's services.
It doesn't directly contain sensitive data, but the stored identifier can be used to track browsing behavior across multiple sites, which raises privacy concerns.
Yes, as a marketing/tracking cookie, it requires the visitor's explicit, prior consent under GDPR and the ePrivacy Directive.