By the careful analysis of the most wide spread attacks compromising host security in the Internet environment, presented in the Chapter, it was shown that existing operating system access control and privilege management mechanisms need to be redesigned to be able to survive in the increasingly insecure environment. The analysis exposed Discretionary Access Control model as the most security critical in current operating systems. Research in the field of computer security, as well as standards developed in the past several years, have recognized Mandatory Security Policies and Mandatory Access Control, in particular, as a must replacement for existing DAC. MAC, in combination with the Least Privilege principle, can not only provide security breach prevention but also breach and damage confinement within a system.