Virus = a small program that some malicious hacker writes that can disrupt the operation of your computer.
There are many different kinds of viruses: Some are extremely dangerous and can erase all of the programs and data
on your computer. Others can noticeably slow down the operation of your computer. Some are relatively innocuous
and just want to travel from computer to computer. Some can cause annoying or salacious messages to appear on the
screen, sometimes only on special days, such as Christmas or Valentine's Day.
There are many ways a virus can move from computer to computer. Some do so using floppy disks, by infecting the index of the plastic magnetic disk inside the hard plastic case of the floppy disk. When you insert the floppy disk into your floppy disk drive and access a file on it, the virus is copied to your hard drive, ready to infect another floppy disk that you put into the floppy disk drive.
Other viruses attach themselves to e-mail messages or infect attachments to e-mail messages and can then find your e-mail address book and automatically mail copies of themselves to everyone in your address book.
There are various ways to protect your computer against viruses, such as the anti-virus programs manufactured by such companies as Symantec ("Norton AntiVirus") and Network Associates ("McAfee VirusScan").
It is an extremely good idea to have one of these programs on your computer and to keep it up-to-date by visiting the manufacturer's web site at least once a month to download the list of new viruses published by the manufacturer. Some virus program manufacturers also have a new service where they will check your hard drive from their web sites when you access their sites.
It is imperative to create regular backups of your data, because some viruses can wipe out all of your data in a flash. If a virus does destroy all of your data, it can cost hundreds of times more than the price of the anti-virus programs to recreate your data or restore your computer to the way it was. (Businesses sometimes have to spend thousands of dollars PER VIRUS ATTACK to get rid of them.)