摘要：当我们评判一个系统是否安全时，不应该只看它应用了多么先进的设施，更应该了解它最大的弱点是什么，因为网络的安全性取决于它最薄弱环节的安全性。

    通过考察近几年在 Internet 上发生的黑客攻击事件，我们不难看出威胁网络安全的基本模式是一样的。特别在大量自动软件工具出现以后，加之 Internet 提供的便利，攻击者可以很方便地组成团体，使得网络安全受到的威胁更加严重。

    隐藏在世界各地的攻击者通常可以越过算法本身，不需要去试每一个可能的密钥，甚至不需要去寻找算法本身的漏洞，他们能够利用所有可能就范的错误，包括设计错误、安装配置错误及教育培训失误等，向网络发起攻击。但在大多数情况下，他们是利用设计者们犯的一次次重复发生的错误轻松得逞的。

    我们可以粗略地将对系统安全造成的威胁归结为 6 大类 : 教育培训问题、变节的员工、系统软件的缺陷、对硬件的攻击、错误的信任模型和拒绝服务。需要指出的是，这几类威胁之间可能会有交叉与重叠之处。另外，一些文献对系统安全的威胁分类方法可能同这里给出的不同，但大多没有本质的区别。

 [关键字] :   网络   系统软件  特洛伊木马

Abstract：When we adjudicate a system whether safety, shouldn't should see only it applied the how advanced facilities, should also understand it biggest weakness is safety that safety that what, because the network is decided by it the most weak link.

    Pass to investigate in the last few years black an attack affairs taken place on the Internet, we are not difficult to see a basic mode for threatenning the network is safe is similar.It is special to appear hereafter in the automatic software in large quantity tool, convenience that add that Internet provide, the aggressor can constitute the group very expediently, making the threat that network safety suffer been serious more.

    Concealing the aggressor in world-wide locations can usually cross the calculate way oneself, doing not need to try each a mistake for possible Key of encrypting , even doing not need to looking for loophole of oneself calculate way, they can making use of mistakes , including to design the mistake and install to install the mistake and educate training error etc., starting to network the attack.But under the majority the circumstance, they are to make use of the design make a to repeat what the mistake of the occurrence is not relaxed to succeed.

    We can return knot as the 6 major type to the system safety the threat that result in roughly then: Education training problem, the employee, system who change of loyalty the blemish of the software, to the attack, false and trustful of model of the hardware with brush-off serve.What demand point out is, this of several threat may have place that cross with the overlap.Moreover, the some cultural heritage divides into section to the safe threat in system the method may give here together out of different, but have no the hypostatic differentiation mostly.

[Key words]： Network ,System software , Trojam horse