A computer virus is a piece of code that makes loaded onto your computer without your knowledge and runs against your cares. The first known occurrence of viruses goes back to 1987 when the ARPANET was pussy by one.
One general misnomer among people is that you can taint your computer just by initiative an email and reading its text. That is not possible; it is usually the files attached to the email that check the virus. The most commercial-gra...