Does your computer system seem to run slower than it should? Does it crash often and display error messages you don't recognize? Play musical tunes you've never heard before? If your computer acts like it's inhabited by ghosts, you may have a computer virus or some kind of spyware.
On the other hand, an unhealthy or overloaded system could cause some of these same problems — particularly sluggish performance. Your hard drive could just be running out of space, or you could have insufficient memory resources for the applications you're running.
So how do you tell the difference between a virus and a system problem? Generally speaking, if you notice sudden, unexpected behavior, like strange sounds coming from your computer or file names you don't recognize, you probably have a virus.
If you think you've contracted a computer virus, you have several options:
Run a disk-repair utility. After you start your computer from the boot disk, run a disk-repair utility. Both Mac and Windows operating systems come with a disk-repair utility that you can use for this purpose. Once you get the computer up and running again, scan your entire system with antivirus software.