Antivirus are small software programs that can spread from one computer even to another and to interfere by means of computer operation.
A contamination might.. corrupt or delete data on your hard drive, use your e-mail process to spread itself to help you other computers, or even erase everything on the hard disk.
Antivirus are often spread by way of attachments in e-mail messages or instant messaging communications. That is why it is crucial that you never open e-mail attachments if you know who it’s from and you simply are expecting it.