The three classes of intruders are:
Masquerader: It can be defined as an individual who is not authorized on the computer but hacks the system’s access control and get access of authenticated user’s accounts.
Misfeasor: In this case, user is authenticated to use the system resources but he misuses his access to the system.
Clandestine user, It can be defined as an individual who hacks the control system of the system and bypasses the system security system.
