Concept:Computer viruses typically cause unusual or harmful behaviour, not improved performance.
Explanation:Symptoms of a computer virus attack include the drive light turning on without any clear reason.
They also include unexplainable printer activity, such as printing jobs appearing by themselves.
Another common symptom is the disappearance of files or the appearance of strange files on the screen.
However, improved processing speed is not a symptom of a virus attack.
In fact, a virus usually slows down the computer instead of making it faster.
Therefore, only the first three listed symptoms are correct.
Answer:Option A: I, II and III only.