A cookie is a small data file that is written to your hard drive when you browse certain Web sites. Cookie files control certain information, such as a random number user ID that the site assigns to a visitor to track the pages visited. Cookies are useful for enabling the browser to remember information specific to a given user. A cookie cannot read data off your hard disk or read cookie files created by other sites. Cookies, by themselves, cannot be used to find out the identity of any user.