A cookie is a packet of information sent by a web server to a web browser. Cookies are generated each time the user visits the website. A message is frequently displayed saying 'cookies are required to access this site' (or some equivalent message). Every time a user visits the website, cookies will have collected some key information about the user. They are able to carry out user tracking and also maintain user preferences (for example, when a user buys an electronic device on a music website, the cookies will have remembered the user's previous buying habits and a message like this often follows: "Customers who bought items in your Recent History also bought...").

Cookies aren't programs but are simply pieces of data. They can't actually perform any operations. They only allow the detection of web pages viewed by a user on a particular website and store user preferences, as described above.

The information gathered by cookies forms an anonymous user profile and doesn't contain personal information (such as credit card numbers or passwords). Because of the information they do collect however, they are subject to privacy and security concerns. Cookies do not in themselves present a threat.