So has your hamster. Your system works fine, but it complains loudly about foreign software. This revolutionary virus does not horse around. Makes it's presence known, but doesn't do anything. Secretly, you wish it would.
Files disappear, only to reappear mysteriously a year later, in another directory.
You know it's guilty of trashing your system, but you just can't prove it. Could be virulent, but it's been around too long to be much of a threat. All files are reported as the same size. Activates every component in your system, just before the whole thing quits. Nothing works, but all your diagnostic software says everything is fine.