Copyright (c) 2002 by Jennifer Vesperman. This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v0.4 or later (the latest version is presently available at http://www.opencontent.org/openpub/).
Computer viruses are hostile programs written to create havoc and mayhem. They can only do damage if you, or some program acting on your behalf, actually runs the virus program. To be absolutely safe from viruses, never run any programs. Of course, that makes the computer rather pointless.
To be reasonably safe, be very careful what programs you run. Buy or download programs from trusted sources, use an up-to-date virus checking program regularly, and definitely before running any newly installed programs.
Be aware of programs which don't look like programs! Microsoft Word documents can have mini-programs in them, called 'macros'. These mini-programs can spread in Word documents. To be safe from macro-viruses, never open someone else's Word document - have the other person export them into another format that doesn't include macros. RTF, or Rich Text Format, is a good one to use.
Email used to be safe, because you had to actually download and save, then manually run, any programs which came in your email. Microsoft decided to enable Outlook to automatically run programs, 'to make email easier to use'. Unfortunately, they made this the default setting. To keep your email safe, turn this off! There is a link at the bottom of this article telling you how.
Java programs on web pages are usually safe, because Java is designed so that web page applets can't write to or read from your own hard drive, only the hard drive on the computer that actually hosts the web page. (Minor exception: web pages can ask your web browser to write 'cookies' onto your hard drive. Because your web browser actually does the work, I can't imagine anyone figuring out how to write a 'cookie' virus. I *think* it's impossible - but I'm learning to say 'nothing's impossible'.)