众所周知，网络是为 广大用户共享网上的资 源而互联的，然而，由 于网络具有开放及共 享的特点，容易引起 网络的安全性问 题，即网络容易受 到外界的攻击甚 至破坏。即使你 已将大楼的门 完全锁好了，但 攻击者还是可以 通过计算机网络 在世界的另一头侵 入你的机器，翻阅机 As we all know, the Internet is for the majority of users to share Internet resources and Internet, however, due to the open and shared network features, easily lead to network security problems, that is, the network vulnerable to attack or even damage the outside world. Even if you have completely locked the building door, but the attacker can still invade your machine through the computer network in the other end of the world,