Differentiate between protection and security.
Operating system contains a collection of objects, software or hardware. All objects have a unique name and can be accessed by a well-defined operations set. Protection problem - make sure that each object is accessed appropriately and only by those processes which are allowed to do so.
Security should notice external environment of the system, and protect this from:
I. Unauthorized access.
II. malicious modification or destruction
III. Accidental introduction of inconsistency.