A small text file (up to 4KB) created by a website that is stored in the user's computer either temporarily for that session only or permanently on the hard disk (persistent cookie). Cookies provide a way for the website to recognize you and keep track of your preferences.
Cookies Are Beneficial
Cookies are commonly used to "maintain the state" of a browser session. For example, users can place items in a shopping cart, switch to another page or even another site, and when they come back, the site recognizes them and the current state of the cart. See state
Cookies contain a range of URLs (addresses) for which they are valid. When the Web browser or other HTTP application sends a request to a Web server with those URLs again, it sends along the related cookies. For example, if your user ID and password are stored in a cookie, it saves you from typing in the same information all over again when accessing that service the next time. By retaining user history, cookies allow the website to tailor the pages and create a custom experience for each individual.
Your Cookies Know You
Quite a bit of personal data may reside in the cookie files in your computer. As a result, this storehouse of private information is sometimes the object of attack (see cookie poisoning
First-Party Personal Cookies
The default settings in your Web browser typically allow "first-party" cookies, but not "third-party" cookies. First-party cookies are created by the website you are visiting and are necessary to keep track of your personal preferences and the current session as explained above.
Third-Party Tracking Cookies
Third-party cookies are created by a website other than the one you are currently visiting; for example, by a third-party advertiser on that site. The purpose of such cookies is usually to track your surfing habits, which is why third-party cookies are considered an invasion of privacy and riskier than first-party cookies.
A Web browser can be configured so that only first-party cookies coming from the originating sites are maintained. It can also be set to prevent all cookies from being stored in your computer, but that severely limits the Web surfing experience. To change settings, look for the cookie options in your browser in the Options or Preferences menu. See Web bug
, cookie file
, Flash cookie
, magic cookie