Abstract: A security system for distributed computer systems with a central computer and remotely located interactive terminals. The security system includes a master security control processor (SCP) which is associated with the central computer, and one or more slave SCPs, each of which is associated with one of the interactive terminals. Clearance at several security levels is required before communications between one of the remote terminals and the central computer is authorized. The security levels are implemented after communications are established to maintain only authorized access to the central computer. One of several unauthorized access modes are implemented when an unauthorized interactive terminal or SCP is identified. All data communicated between the master and slave SCPs is encrypted for security.