Viruses are computer programs or scripts that attempt to spread from one file to another on a single computer and/or from one computer to another, using a variety of methods, without the knowledge and consent of the computer user. A worm is a specific type of virus that propagates itself across many computers, usually by creating copies of itself in each computer's memory. Many users define viruses simply as trick programs designed to delete or move hard drive data, which, strictly speaking, is not correct. From a technical viewpoint, what makes a virus a virus is that it spreads itself. The damage it does is often incidental when making a diagnosis. The most common method used for spreading a virus is through e-mail attachments.
The most common tool used to mitigate the risk and danger of this threat is using a virus scanner which attempts to scan a computer program before it runs. Another tool against viruses is common sense. Don't open an e-mail from an unknown or suspicious source unless you know the risk of opening the attachment. Avoid the risk of malware with the following: Keep your computer software current. Both the operating system and the anti-virus application must be updated on a regular basis. Only download updates from a reputable source.
Always weigh the risks of installing something on your computer. This includes reading the fine-print license! Install and use a firewall.
"Prevention is always better than cure."