The essential component of a virus is a set of instructions which
计算机病毒的基本组成部分是这样一组指令，
when executed ,spreads itself to other ,previously unaffected, programs or files.
当这组指令被执行时，它就会被传播到本来没受过影响的程序或文件上。
First , it copies itself into previously uninfected programs or files.
第一种作用是要把它自身拷贝到以前未受感染的程序或文件上。
Second (perhaps after a specific number of executions, or on a specific date) it executes whatever other instructions the virus author included in it.
第二种作用是（也许是在某特定的执行次数以后，或者在某个特定日期）执行病毒作者所隐含在其中的别的什么指令。
Depending on the motives of the virus author, these instructions can do anything at all.
根据病毒作者的动机，这些指令完全能做出任何事情。
including displaying a message ,erasing files or subtly altering stored data.
包括：显示某种信息，抹去某些文件或微妙地改变存储的数据。
In some cases ,a virus may contain no intentionally harmful or disruptive instructions at all.
在某些情况下，某种病毒可能一点没有包含什么故意有害的或破坏性的指令。
Instead , it may cause damage by replicating itself and taking up scarce resources, such as disk space, CPU time ,or network connections.
而是通过自身的重复和占去某些值得的资源（如磁盘空间、CPU时间或网络连接等）来造成破坏。
Let us now examine a particular sequence of events by which virus could enter an organization and spread within it .
现在让我们来观察一个特殊系列事件，通过这些事件，病毒进入一个机构并广为传播。
Suppose that the organization hires an outside person to come in and perform some work.
假设这个机构在外面雇佣了一个外来人员来完成这项工作。
Part of that person's work involves working on one of the organization's personal computers.
这项工作的一部分要在该机构的一台个人计算机上操作。
The person brings in a few programs to aid in this work, such as a favorite text editor.
此人为了有助于工作的进行，带来了一些程序，如一个适用的文本编辑程序。
Without the person having realized it ,the text editor may be infected with a virus.
在无人意识到的情况下，这个文本编辑程序可能会染上了一种病毒。