No one wants to own a computer infected with a nasty virus. That’s why it’s very important to practice safe computing habits and to install reliable anti-virus software.

Good news is, you can avoid most malware just by paying attention and staying away from a few common traps. If your anti-virus software is up to date, you should be in pretty good shape.

But once in a while, computer viruses get beyond our defenses. Maybe our anti-virus software is out of date or has been compromised by a particularly clever bit of code. Perhaps we clicked on a link by accident and activated a virus. Or someone else used our computer and downloaded some malware by mistake.

How do you know if your computer has been hit by a computer virus? Here are 7 signs.

  1. Speed is compromised. Does your computer seem to run much more slowly than it used to? This could be the result of malware as the malicious code begins to drain your computer’s processing resources. If you aren’t running a resource-heavy application but your computer is very slow, you might have a computer virus.
  2. Your modem lights are constantly moving, even if you are not using your computer. If you don’t have any programs running and your modem transfer lights are constantly blinking, you may have a virus that is transmitting data over the network.
  3. You get queer messages. Strange messages indicating that you can’t access certain drives on your computer are another sign that something is wrong. In a similar vein, applications that won’t run or files that won’t open may also be the result of infection.
  4. It takes your computer to boot up. If you start noticing that your computer takes significantly more time than usual to start, a virus may be slowing down the startup process. If you can’t log in to Windows, even with the correct log in information, a virus has most likely taken over the log in process.
  5. Instability or Crashing. If your computer has become unstable, that’s a sign that something’s wrong. Some malware messes with important files that keep your computer running properly. That could cause your computer to crash. If your computer crashes when you try to run a specific application or open a particular file, which tells you that something has corrupted the data. It could be malware.
  6. Your hard drive activity is unusual. If you aren’t running any programs and your hard drive light is constantly turning on and off, or you can hear the hard drive working, you may have a virus that is working in the background.
  7. If you notice that file sizes are fluctuating even if you aren’t accessing those files, that’s another sign of a computer virus. And finally, if you access menus and their appearance is odd or distorted, you could be the victim of a malware attack.