Infoseek pioneered using this technology. Infoseek tracks what keywords you search by so they can build up a profile of you over time. It stores this information encoded in your cookie file. Infoseek uses this information to serve up advertisements that you are more likely to respond to. I might even see high-tech ads when I search for information on the New York Yankees because Infoseek knows that I am still likely to respond to the ad.
Cookies are a very simple but extremely important tool.
Many sites that require entrants to use cookies so that security can be kept at a maximum. Sites like BirdgePath , the job finder server, and Guestimate employ cookies to make their system more secure by tracking a user as she travels the site. When you log in, you receive a cookie that identifies you to the server. It can then pull up information about you from the database and store characteristics on you like how many times you logged in or what careers you might be interest in. Using cookies when programming web sites is fairly complicated, but they are transparent to the visitor.