How do computer viruses sperad?

Answer 1

When a virus infects a computer it add registry keys to enable its execution at EVERY startup (until registry key is romoved). In most cases the virus opens email applications on your computer, such as outlook and messenger. If the virus is more sophisticated it may look in IE temporary files in your browser and use that.

If however it cannot access your email it monitors that webpage until you log into it again and records the username and password (Keylogger). And then puts the code in an email and sends it to the people in your address book. When the email is opened the virus infects the computer it does the same thing.

Every time i get an email i look at the message source. It opens the message safely and lets you see the code/writing in the email. If you see unusual code or line of jumbled up letters and numbers odds are the email is infected and should be deleted immedieatley.