WHMCS uses cookies to maintain session state and store small amounts of data on visitors’ computers or devices. Cookies are small text files that most websites on the internet store on your device and use to improve your overall experience.

WHMCS uses two types of cookie:

Session cookies — These expire when you close your browser. They do not remain on your computer. Persistent cookies — These stay on your computer for a defined period of time.

WHMCS creates the following cookies when you use the WHMCS client area:

WHMCSInstanceID — This is the most common cookie that most PHP-based websites will use. This stores the unique session ID for each visitor and enables variables to pass between page loads. The cookie only contains a reference to a session on the web server. The user's browser won't store any personal information. This is a session-only cookie, so it expires as soon as you close the browser.

WHMCSAffiliateID — WHMCS sets this cookie when an affiliate refers a customer to you. It stores the ID of the affiliate that made the referral so that if the customer places an order within the next 90 days following the referral, the affiliate receives credit for it. It is a persistent cookie.

WHMCSLinkID— WHMCS only sets this cookie if you use the link tracking (Utilities > Link Tracking). It remembers the link the visitor followed to get to your website, and the system uses it when receiving an order, to be able to associate the conversion with a link to be able to provide stats such as the conversion rate of your links. It is a persistent cookie.

WHMCSUser — WHMCS uses this cookie for the remember me functionality of the client area. The system only sets it if a client chose to have the system remember their details, ensuring that they don't need to log in multiple times. It is persistent and lasts for 365 days, or until logout.