Abstract: A usage based pattern authenticator for monitoring and reporting on user usage patterns in an operating system using a set of security rules and user usage patterns. This computer system security tool authenticates users at the operating system level in multi-user operating systems. It supports system administrators in limiting the ability of unauthorized users to disrupt system operations using a neural network and set of rules to track usage patterns and flag suspicious activity on the system. The data collection mode collects and stores usage patterns of authenticated users. The training mode trains an artificial neural network and sets the interconnection weights of the network. The production mode monitors and reports on usage patterns, and optionally performs automatic responses when confronted with non-authenticated users.