A system for controlling access to a computer. Memory-resident software logic cooperates with a remote electronic key device coupled to the computer's processor, through the printer port, to disable the computer unless an authorized key is inserted in the key device. The logic is executed in the processor responsive to the computer's system timer interrupt for continuous monitoring capability. Until a user inserts an authorized key, or upon removal of the key, the logic suspends operation of any application programs, the monitor is blanked and the mouse, keyboard and floppy disk drive are disabled. A record is stored in memory of authorized users and user audit information. Utility menu options are used to add or delete user keys, display access and usage records and to customize the number and selection of I/O devices to be disabled by the system.