In Browsers Tips . Cookies let our Website recognize previous visitors to our web page, record a visitor's progress from page to page, and recall certain information a visitor entered previously. For instance, a cookie may store your password, or note that you're interested in electronics. We may also use tracking images and applets to collect the same information. To keep your name and password for sites you visit that need this data.
Some sites keep the data at their site, some use a cookie.
An example of this is Yahoo free-mail. If you delete cookies as recommended here, you will have to enter the name and password next time you access the e-mail. Some sites can use cookies to record your browsing habits for future use or collecting marketing data and know something about you automatically when you revisit their site. Many cookies are shared among multiple sites. Your computer can be scanned for hardware and software and the data entered in a cookie again for marketing purposes.