Cookies are used for many different reasons; storing your preferences, generally improving the user experience and making the interaction between you and the website faster and easier. For example, if you have to log in to a web site then some information has to be maintained to indicate that you had logged in on a previous page.
Cookies may be set by the website you are visiting (‘first party cookies’) or they may be set by other websites who run content on the page you are viewing (‘third party cookies’).
What is in a cookie?
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 to do if you don’t want cookies to be set
Some people find the idea of a website storing information on their computer or mobile device a bit intrusive, particularly when this information is stored and used by a third party without them knowing. Although this is generally quite harmless you may not, for example, want to see advertising that has been targeted to your interests. If you prefer, it is possible to block some or all cookies, or even to delete cookies that have already been set; but you need to be aware that you might lose some functions of that website.
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?
Cookies are stored on the computer's hard drive. They cannot access the hard drive - so a cookie can't read other information saved on the hard drive, or get a user's e-mail address etc. They only contain and transfer to the server as much information as the users themselves have disclosed to a certain web site.
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.