The protection of Command, Control, Communications, Computers, and Intelligence (C4I) systems during times of both war and peace is a major issue. There are many traditional mechanisms to provide such protection, but they have many limitations related to inaccuracy and false alarms. In this paper, we discuss possible types of attacks in the context of C4I systems, including Denial-of-Service (DoS), Distributed Denial-of-Service (DDoS), Probe, User-to-Root (U2R), and Root-to-Local (R2L) attacks, and propose a fundamental model to prevent such attacks.