A computer system which is configured to load executable programs. This configuration first accepts an operator defined key; withdraws an encrypted executable program from memory; and, using the operator defined key, decrypts the encrypted executable program into a functional executable program. It is this functional executable program which is used by the processing unit. During shutdown, each executable program is checked to see if it was derived from an encrypted executable program; those that aren't, are verified as being legitimate by the operator prior to their storage into the memory.