A system and method for an access code issuer to receive an on-line application including certain personal information from a user of a computer network such as the Internet, to independently operatively connect to a database and obtain or verify demographic and additional personal information regarding the user, and issue an access code to the user. The user enters this access code when accessing various nodes or websites of a plurality of affiliated content providers. The content providers obtain or verify the user's demographics by operatively connecting to the access code issuer, thereby obtaining or verifying the demographics of the visitor to its site without requiring the visitor to enter his or her demographic information or to independently provide proof thereof to the content provider. The content provider can then customize the presentation and advertising on its site according to the demographics of the user, and/or can restrict access to its site or portions thereof based on demographics or other information regarding the user. Authentication is provided using a portion of a social security number.