is a malicious type of computer virus
for "malicious software." It's a "catch all" term for software designed
purposefully damage or disrupt a system. It could be a virus that
spreads throughout your system, a Trojan Horse that is "triggered" on a
certain date, or even Spyware that secretly sends your personal data to
someone monitoring from afar. Its different from something like a
Pop-up because, while it is an annoyance, it does not damage your PC.