Antivirus are small software programs that should spread from one computer to another one and to interfere using computer operation.
A contamination might.. corrupt or delete data on your hard drive, use your e-mail process to spread itself to other computers, or even erase everything upon your hard disk.
Antivirus are often spread just by attachments in e-mail messages or instant messaging information. That is why it is necessary that you never open e-mail attachments until you know who it’s from therefore you are expecting it.