How DoubleClick works
DoubleClick is the largest provider of Internet advertising. In the course of providing advertisements to web sites, it collects information about web site visitors. When a user opens a web site to which DoubleClick supplies advertising, the users computer sends a message to the web siteís server requesting that it send it the desired web page and it also deposits a cookie on the userís computer that links the userís computer to the DoubleClick server, which sends the advertising that belongs on that web page. The DoubleClick server contains a profile of the user which contains data about the user complied via cookies and other tracking technologies. The server uses the profile to target advertising to fit the preferences of the particular user, and it also updates the profile in light of the userís current online behavior.