Writers say “To write a good book, first tell them what you are going to tell them, then tell them, then tell them what you told them.” This is the “what we're going to tell you” part. Chapter 1, “An Overview of Computer Security,” presents the underpinnings of computer security and an overview of the important issues to place them in context. It begins with a discussion of what computer security is and how threats are connected to security services. The combination of desired services makes up a policy, and mechanisms enforce the policy. All rely on underlying assumptions, and the systems built on top of these assumptions lead to issues of assurance. Finally, the operational and human factors affect the mechanisms used as well as the policy.