Since cookies are often deleted from the visitor’s machine they are not the most reliable method for tracking devices. This is why ClickGUARD uses a proprietary tracking mechanism that provides the best results.
ClickGUARD generates an anonimyzed unique device ID for every visitor's browser, that is used for tracking. As opposed to using cookies, ClickGUARD is using browser local storage to store a reference to the tracking profile (device ID).
Local storage is used to track visitors across multiple ad clicks, campaigns, keywords, etc. This information is later used to detect repetitive ad clicks from the same browser (device).