What is the __qca cookie?
__qca is an HTTP cookie set by Quantcast, a company specializing in audience measurement and web traffic analytics, used by many publishers and advertisers worldwide. The cookie usually appears on the visited website's own domain (a first-party cookie) when the page loads the Quantcast measurement script.
It is typically set on a user's first visit to a site using Quantcast Measure or related audience analytics services, and reused on subsequent visits to recognize the same visitor.
What data it stores
__qca stores a unique, automatically generated identifier assigned to the visitor's browser. This identifier does not typically contain direct personal data (such as a name or email address), but it is considered an online identifier and can be linked to a user's browsing behavior.
The exact value format may vary and is not publicly documented in detail by Quantcast. Data collected through this cookie is transmitted to Quantcast's servers for processing and statistical aggregation.
What it is used for
The cookie's main purpose is audience measurement: Quantcast uses __qca to distinguish unique visitors, estimate repeat visits, and build aggregated profiles of a site's traffic (for example, estimated demographic categories, interests, and visit frequency).
For the website owner, this data provides insight into the site's audience, useful for reporting and, in some cases, content planning or advertising partnerships.
Does it require consent?
In CookieFix's classification, __qca falls under the statistics (analytics) category. Since it is not strictly necessary for the site's technical operation, under the GDPR (Regulation 2016/679) and the ePrivacy Directive 2002/58/EC (as transposed locally, e.g. via Romania's Law 506/2004), this cookie requires the visitor's prior consent before being set.
Website owners must list it accurately in their cookie policy, group it under the statistics category in the consent banner, and make sure the Quantcast script does not load before the visitor gives consent.
How to block or delete __qca
A visitor can manually delete or block __qca through browser settings (Chrome, Firefox, Edge, Safari) by clearing the site's cookies or enabling blocking of third-party/analytics cookies. They can also decline the „statistics” category in the site's consent banner, if granular choices are offered.
- Website owners using a platform like CookieFix can automatically block the Quantcast script until the visitor explicitly accepts the statistics category, preventing the cookie from being set without consent.
- Blocking can also be configured manually, by conditionally loading the Quantcast script based on consent status.
Frequently asked questions
It does not typically store direct personal data like your name or email, but rather an identifier used for audience statistics. It is still an online identifier treated as personal data under GDPR.
Yes, because it is a statistics cookie, not a strictly necessary one. The site must obtain your consent before setting it, in line with ePrivacy and GDPR rules.
Its typical duration is about one year from when it is set or last updated, though this can vary depending on the specific Quantcast service configuration.
You can inspect stored cookies through your browser's privacy/site data settings, or use developer tools (the Application/Storage tab).