A cookie is a piece of information in the form of a very small text file that is placed on an internet user's hard drive. It is generated by a web page server, which is basically the computer that operates a web site. The information the cookie contains is set by the server and it can be used by that server whenever the user visits the site. A cookie can be thought of as an internet user's identification card, which tell a web site when the user has returned.
What is the purpose of cookies?
Cookies make the interaction between users and web sites faster and easier. Without cookies, it would be very difficult for a web site to allow a visitor to fill up a shopping cart or to remember the user's preferences or registration details for a future visit.
Cookies enable web sites to monitor their users' web surfing habits and profile them for marketing purposes (for example, to find out which products or services they are interested in and send them targeted advertisements).
Are cookies dangerous?
No. Cookies are small pieces of text. They are not computer programs, and they can't be executed as code. Also, they cannot be used to disseminate viruses, and modern versions of both Microsoft Internet Explorer and Netscape browsers allow users to set their own limitations to the number of cookies saved on their hard drives.
Can cookies threaten users' privacy?
A server cannot set a cookie for a domain that it is not a member of. In spite of this, users quite often find in their computer files cookies from web sites that they have never visited. These cookies are usually set by companies that sell internet advertising on behalf of other web sites. Therefore it may be possible that users' information is passed to third party web sites without the users' knowledge or consent, such as information on surfing habits. This is the most common reason for people rejecting or fearing cookies.