Sites deliver targeted advertising through ad serving technologies. Some sites have their own, but for the most part, sites use other companies who specialize in this form of technology to deliver their ads for them. Regardless of the form of ad serving, to deliver personalized content, these sites must all use a fairly simple technology called cookies.
What are cookies?
How are cookies used by networks and ad servers?
When you are first served an ad by an ad server, it gives your browser a unique number and records that number in the cookie file of your computer. Then, when you visit a Web site on which that server is delivering ads, it can then read this number to help deliver relevant advertising to you.
Cookies allow networks and ad servers to: