Access control software

Definition
Access control software is

"software, which is external to the operating system, [that] provides a means of specifying who has access to a system, which has access to specific resources, and what capabilities authorized users are granted."

Overview
Access control software can generally be implemented in different modes that provide varying degrees of protection such as denying access for which the user is not expressly authorized, allowing access which is not expressly authorized but providing a warning, or allowing access to all resources without warning regardless of authority.