Abstract: A method of restricting access to data maintained on a server computer by one or more authorized, networked client machines includes the step of installing a client-side software program on the client machine for generating a client machine-specific identifier determined by particular characteristics of the client machine. The machine-specific identifier is used by the server administrator to generate a unique password, which the user enters into the client-side software program. Server-side software is embedded on protected Web pages of the server computer that hosts the protected Web site. When a user desires access to protected content, the client-side software is prompted to re-generate its machine-specific identifier and valid client password list for comparison with the password previously entered by the user. Access is granted if they correspond, and denied if they do not.