There are many different strains of flu virus.

流感病毒有很多不同类型。

HIV, the virus believed to cause AIDS.

被认为会引发艾滋病的HIV病毒。

Hackers are said to have started a computer virus.

据说黑客们已经开始传播一种新的电脑病毒。

By the time a virus is detected it will almost certainly have infected other disks.

等检测到病毒时，几乎可以肯定其它磁盘也已经被感染了。