1.) Any program on your computer that reproduces its code
2.) Any program on your computer that completely fucks it up and disables its ability to work properly
3.) A said program that you probably got when you opened an e-mail you didn't know who it was from or downloaded something that you didn't know what it was
Person 1: My computer keeps crashing, I think it has a virus.
Person 2: Did you open any emails you recieved from a stranger?
2: Did you download any strange files?
2: Are you running Windows?