DoubleClick uses cookies in order to improve their publicity. They normally use them to direct publicity according to the content that is relevant for the user, to improve the return on performance information and to prevent ads that the user has already seen.

Every cookie´s ID from DoubleClick is of importance for these applications. For example, DoubleClick uses a cookie’s ID in order to create a register of all ads that are shown in each browser. Once DoubleClick publishes an ad in a browser, DoubleClick can use that browsers cookie ID in order to check DoubleClick’s ads that have already been shown there. That way DoubleClick prevents showing ads the user has already seen. In the same way, the cookie’s ID allows DoubleClick to register conversations related to applications, like for example when a user sees one of DoubleClick’s ads and afterwards uses the same browser to visit that client’s Website and purchases something. DoubleClick’s cookies don’t contain information about personal identification. Sometimes the cookie contains an extra identification that looks like the cookie’s ID. This identification is used in order to identify an advertising campaign to which the client hasn’t been exposed before; but DoubleClick doesn’t keep personal information about identification in the cookie.