Automated system for identifying authorized system users

An apparatus for identifying authorized users of a secure system, comprising:

• (A) user prompting means for prompting a user of said secure system to enter a personal identification code into said secure system;
• (B) personal identification code receiving means, coupled to said user prompting means, for receiving into said secure system a first digital signal representative of said personal identification code entered by said user;
• (C) storage means, coupled to said personal identification code receiving means, for storing a list of authorized personal identification codes;
• (D) comparing means, coupled to said storage means, for comparing said personal identification code entered by said user against said list of authorized personal identification codes;
• and
• (E) user authorizing means, coupled to said comparing means, for receiving a second digital signal identifying whether said user is an authorized user of said secure system, said user being identified as an authorized user of said secure system only if said personal identification code entered by said user is present in said list of authorized personal identification codes;
• wherein each personal identification code on said list of authorized personal identification codes is arranged in a personal identification code format that includes a plurality of core digits and a plurality of check digits, and wherein a first of said check digits has a value that is dependent upon a first group of two or more core digits, and a second of said check digits has a value that is dependent upon a second group of two or more core digits, said first group of two or more core digits being different from said second group of two or more core digits.