Cookies are small pieces of text stored on a user's computer by a web browser. They allow the browser to "remember" things e.g. which page you last visited, your login name, your preferences and so on. Cookies are essential to the operation of most web transactions. Some people get hysterical about cookies, but they are harmless and perform a vital function. However, one type of cookie — a tracking cookie — allows web sites to track some of your browsing history.

There are three types of cookies: session cookies, persistent cooking and tracking cookies.

Session cookies are critical to the web’s usefulness. HTTP is a “stateless” protocol. That means it has no memory; it treats each request as entirely separate from all others. Cookies provide “memory.” They allow a web server to customize the next page based on pages accessed previously. Cookies are essential in shopping carts and online purchases. See below for an example of trying to perform a transaction without cookies:


Persistent cookies save time and allow customization. They store login information, allowing you to revisit sites with authentication without logging in every time, such as the New York Times or the Wall Street Journal. They also allow customized content. For example, when you visit the web server recognizes you and provides customized recommendations.

Tracking cookies provide information to advertisers. Tracking cookies are persistent. They are updated by each web site you visit in a network.
A third party site collects the information from all the sites in the network. This information can be used to create a profile of your interests. The profile is used to target advertising relevant to your interests.

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