Antivirus are small software programs that should spread from one computer to an alternative and to interfere by using computer operation.
A disease might.. corrupt or delete data on your computer, use your e-mail program to spread itself to be able to other computers, or even erase everything on your hard disk.
Antivirus are often spread by attachments in e-mail emails or instant messaging email. That is why it is crucial that you never open e-mail attachments until you know who it’s from and you are expecting it.