What is the __ar_v4 cookie?
__ar_v4 is an HTTP cookie set by AdRoll, a digital advertising and retargeting platform owned by NextRoll, widely used by e-commerce and marketing sites to run personalized ad campaigns.
The cookie typically appears on a site when an AdRoll pixel or script is integrated (directly, or through an e-commerce platform, as part of a retargeting campaign) and is set on the .adroll.com domain, making it a third-party cookie from the perspective of the site being visited.
What data it stores
__ar_v4 stores an identifier used by AdRoll to recognize the visitor's browser across visits and across multiple sites that use the AdRoll network. The exact value format is not publicly documented in detail and may vary; it typically does not contain directly identifiable data such as a name or email address.
Data collected via this identifier is sent to AdRoll/NextRoll servers, where it is used to build behavioral profiles and serve relevant ads on other sites within the network.
What it is used for
The main purpose of __ar_v4 is ad retargeting: it allows AdRoll to identify users who have visited a site and later show them ads for that site on other web pages or social networks.
For the site owner, this cookie supports visitor recovery campaigns (for example, cart abandonment) and measurement of ad effectiveness by tracking conversions generated.
Does it require consent?
__ar_v4 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 the visitor's prior consent before being set, since it involves tracking behavior across multiple sites.
The site owner must disclose this cookie in the cookie policy, obtain explicit consent via the consent banner before the AdRoll script loads, and allow visitors to easily withdraw consent.
How to block or delete __ar_v4
A visitor can delete or block __ar_v4 through the browser's privacy/cookie settings, use tracker-blocking extensions, or opt out of personalized ads directly via the AdRoll/NextRoll opt-out page.
For the site owner, the safest approach is using a CMP like CookieFix, which automatically blocks the AdRoll script until the visitor consents to the marketing category, preventing the cookie from being set prematurely.
Frequently asked questions
It is not technically harmful, but it is a tracking cookie used for behavioral advertising, which raises privacy concerns if set without consent.
The typical duration is 1 year from when it is set or last updated, though the exact period may vary depending on the AdRoll campaign configuration.
It is a third-party cookie, since it is set on the .adroll.com domain rather than the domain of the site the user is visiting.
Yes, as a marketing cookie requiring consent, it must be clearly disclosed in the cookie policy along with its purpose, provider, and duration.