How cookies are used

From Microsoft Internet Explorer Help

A cookie is a file created by an Internet site to store information on your computer, such as your preferences when visiting that site. For example, if you inquire about a flight schedule at an airline's Web site, the site might create a cookie that contains your itinerary. Or it might only contain a record of the pages you looked at within the site you visited, to help the site customize the view for you the next time you visit.

Cookies can also store personally identifiable information. Personally identifiable information is information that can be used to identify or contact you, such as your name, e-mail address, home or work address, or telephone number. However, a Web site only has access to the personally identifiable information that you provide. For example, a Web site cannot determine your e-mail name unless you provide it. Also, a Web site cannot gain access to other information on your computer.

Once a cookie is saved on your computer, only the Web site that created the cookie can read it.