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What are Cookies? • A cookie, also known as a web cookie, browser cookie, and HTTP cookie, is a piece of text stored by a user's web browser. A cookie can be used for authentication, storing site preferences, shopping cart contents, the identifier for a server-based session, or anything else that can be accomplished through storing text data • The web server tracks session cookies (cookies for the page content) • The ad server tracks ad cookies (cookies for the displayed ad)
Drawbacks of Cookies • Multiple computers • Each computer has a browser and each is counted (the same viewer can be counted twice) • Multiple users on same computer • If multiple people use the same computer (i.e. family with their home computer), the cookies will undercount those people and treat them as one • Cookie deletion • If you delete your cookies, it will count you as a different person each time (estimates are that 10%-30% cookie deletion)