What is the C cookie?
C is an HTTP cookie set by Adform, one of the major European advertising technology (adtech) providers used for delivering, targeting, and measuring online ads. The cookie is set on the .adform.net domain, meaning it is not placed directly by the visited website but by a third-party script or tag (for example, a tag management container or an ad pixel) loaded on the page.
This cookie typically appears when a site runs advertising campaigns, remarketing, or integrations with DSP/SSP platforms that rely on Adform's infrastructure to identify and track visitors for advertising purposes.
What data it stores
C is generally used as an identifier associated with the visitor's browser within the Adform ecosystem, allowing the same visitor to be recognized across subsequent visits or across different sites within the advertising network. The exact format of the value is not publicly documented in detail and may vary; it typically does not contain directly identifying data such as a name or email address, but it is still considered personal data under GDPR because it enables tracking of online behavior.
Data collected through this cookie is sent to Adform's servers and may be used for advertising profiling across its partner network.
What it is used for
The main purpose of the C cookie is targeted advertising: Adform uses it to recognize visitors, measure campaign performance (impressions, clicks, conversions), and apply frequency capping so the same user isn't shown the same ad too often.
For website owners, the presence of this cookie is usually linked to an active advertising integration (affiliate network, remarketing, or programmatic ad exchange) and supports the effectiveness of marketing campaigns run through Adform or its connected partners.
Does it require consent?
C is classified as a marketing/advertising cookie. Under Romania's Law 506/2004 (transposing the ePrivacy Directive) and the GDPR, this type of cookie requires prior, explicit, and freely given consent from the visitor before it can be placed in the browser.
- The site owner must list this cookie in the cookie policy, including the provider (Adform), purpose, and duration.
- The script that sets C must be technically blocked until consent is obtained, not just visually hidden in the banner.
- Refusing consent must not affect basic access to the site's content.
How to block or delete C
A visitor can manually delete or block the C cookie through browser settings (Chrome, Firefox, Edge, Safari), under the cookie and site data management section, by searching for the domain adform.net. Ad-tracker blocking extensions or private browsing mode can also be used.
For site owners, technical blocking before consent is mandatory, not optional. A CMP such as CookieFix can automatically detect the Adform script and block it by default until the visitor explicitly accepts the marketing category, preventing non-compliant placement of the cookie.
Frequently asked questions
It's a marketing cookie set on the .adform.net domain, used by the Adform advertising platform to recognize visitors and deliver targeted ads.
The typical duration is 1 month, after which the cookie expires automatically unless reset by a new interaction with the Adform network.
Yes, as a marketing/advertising cookie it requires prior visitor consent under Romania's Law 506/2004 and the GDPR.
You can delete or block it through your browser's privacy settings by searching for the adform.net domain, or use an ad-tracker blocking extension.