Cookies were created to carry information from one web page access to another so that things like user preferences and password access could be applied for an entire online session. The cookie is a means to identify you as a visitor to a web site, but information that you supply to the site, such as preferences or demographic information, may be stored on the site's computers rather than in the cookie on your computer. In many instances, a cookie contains merely an arbitrary identifier which points to records in the website owner's database. Yet, increasing numbers of individuals have exclusive use of a computer and a cookie placed on such a machine identifies an actual individual. As in other arenas, companies use various tactics to get personal data and demographic information out of consumers.
Contests are a common such scheme both online and off.