Although this rule will not protect against virus infection, it will allow you to protect your valuable data in case your computer becomes infected (or, as an added bonus, if you have any other problems with your hardware). Whether or not it was a virus that caused your system to malfunction, the only thing that matters is that unless you back up important data, you may lose years of hard work. That is why it is advisable to back up your most valuable data using external media, such as diskettes, MO disks, magnetic tapes, CDs, etc. In this case, whatever might happen, you will always be prepared. (For added protection, the back-up copies should always be stored in a separate location away from the working copy. That way, in case of fire, or other destructive occurrence, the back-up copy will still be safe.)