A method determines a user demographic profile of an anonymous user that visits one or more websites of a predetermined group of websites. The method includes determining whether an anonymous user's computer has user identification data installed thereon. Determining whether the user identification data is installed is performed upon the anonymous user visiting a website of the predetermined group of websites. The user identification data is unique to the anonymous user. The method further includes installing the user identification data on the anonymous user's computer if the anonymous user's computer does not have the user identification data installed thereon. The method further includes generating a first record of visits by the anonymous user to the websites of the predetermined group of websites. The method further includes providing one or more website profiles comprising demographic characteristics of each website visited by the anonymous user of the predetermined group of websites. The method further includes calculating an estimated user demographic profile of the anonymous user by using the first record of visits by the anonymous user and the one or more website profiles.