Understanding cookies

A cookie is a tiny file placed on your computer at the request of a Web site. The vast majority of cookies are perfectly harmless and are necessary for using certain types of sites. Most often, cookies are used to keep you signed into a Web site that requires logging in. When you log in, a cookie is created that contains information about your current session. Typically, this is just some randomly assigned number that contains no information about you or your computer.

As you browse from one page to the next within the site, the Web server checks the cookie to see whether you're already logged in. If you are logged in, it doesn't ask you to log in again. If it weren't for cookies, you'd have to log in every time you switched from one page to the next within the Web site. That would be a major pain.