Cookies are messages that Web servers pass to your Web browser when you visit Internet sites. Your browser stores each message on the local hard drive. When you request another page from the web server that sent the cookie, your browser sends the cookie back to that server. These files typically contain information about your visit to the Web page, as well as any information you've volunteered, such as your name and interests. Cookies are assigned expiration dates, but depending upon the date they may persist for years on your computer.
Cookies are most commonly used to track Web site activity. When you visit some sites, the server gives you a cookie that acts as your identification card. Upon each return visit to that site, your browser passes that cookie back to the server. In this way, a Web server can gather information about which Web pages are used the most, and which pages are gathering the most repeat hits.
Cookies are also used for online shopping. When you visit an online store, you often must fill out a form that includes your name, address, phone number, and other information. To avoid re-entering this information each time you visit the store, the server may issue you a cookie containing this information. Upon your next visit to the store, this cookie automatically supplies all necessary information for you.
Only the Web site that creates a cookie can read it. Additionally, Web servers can only gain information that you provide.
Webmasters have always been able to track access to their sites, but cookies make it easier to do so. In some cases, cookies come not from the site you're visiting, but from advertising companies that manage the banner ads for a set of sites (such as DoubleClick.com). Cookies from these types of sites often assign you a user I.D., and may use this to develop detailed profiles of the people who select ads across their customers' sites.
Accepting a cookie does not give a server access to your computer or any of your personal information (except for any information that you may have provided, as with online shopping). Servers can only read cookies that they have set, so other servers do not have access to your information. Also, it is not possible to execute code from a cookie, and not possible to use a cookie to deliver a virus.
If cookies were disabled, simply browsing to a webpage alone returns information to the Web server such as your IP address, operating system, web browser, and even the page that you used to link to the current page. On the other hand, cookies can send additional information to a website, such as a history log of web sites you have visited.
The bottom-line is that cookies can reduce your anonymity, and you need to decide if you prefer to sacrifice the convenience of customized web pages to maintain that anonymity.
You can implement a "partial ban" of cookies by setting your web browser to prompt you each time that a web server attempts to create a cookie on your computer. You can decide case-by-case whether you care to accept a cookie or not.
Some web browsers can be set to only maintain a cookie until the browser is exited.
In today's World Wide Web, cookies have become so common, you may find that you have hundreds of them stored on your computer. Cookies are stored in locations specific to an operating system and web browser. Use the following documents to manage cookies on your computer.