For better or for worse, most computer systems are not run that way today. Security is, in general, a trade-off with convenience, and most people are not willing to forgo the convenience of remote access via networks to their computers. Inevitably, they suffer from some loss of security. It is our purpose here to discuss how to minimize the extent of that loss. The situation is even worse for computers hooked up to some sort of network.
Networks are risky for at least three major reasons.
First, and most obvious, more points now exist from which an attack can be launched. A second reason is that you have extended the physical perimeter of your computer system. In a simple computer, everything is within one box. The CPU can fetch authentication data from memory, secure in the knowledge that no enemy can tamper with it or spy on it. This is not the case in a network.