Today's media seem to be filled with news about many different
forms of computer viruses, probably because these pesky electronic
infections are so mysterious.  The most common are:

This infection is really a small computer program that 
imbeds itself inside a legitmate piece of software, such as a 
spreadsheet or E-mail program.  Each time the program runs, the virus
runs too, and it will usually either try to reproduce (by locating
another program on your hard drive in which to imbed itself) or cause
mischief with your hard drive---erase programs, delete certain file
types, etc.

An E-mail virus makes its way across the Internet 
by posing as an innocent attachment to a normal-looking E-mail.  Once
the attachment is downloaded by the unsuspecting recipient, the virus
will do its damage and then usually try to replicate itself by sending
itself to every address listed in the recipient's address book.

A worm, like a virus, is a small computer program.  As its
name implies, it inches across computer networks, looking for specific
security holes (weak points in a software program; usally software 
that makes up part or all of a Network Operating System) in which to
replicate itself.

A copy of a worm scans the network for software weaknesses that
their creators have discovered and, as programmed, either wreaks havoc
and/or replicates itself and moves on to the next computer with the
same security hole.

A Trojan horse is a software program that claims
to be one thing---a game or utility program---but isn't.  It does
damage when you run the program.  Trojan horses do not replicate
automatically.

NIMDA is both a virus and a worm---it is a small program that 
attaches to other programs and depends on the Internet to "get around."
If you are using Windows 95, 98, Millennium, NT, or 2000 software,
you are vulnerable to this virus.  Your computer can be infected if 
you:

• download E-mail attachments
• visit Web sites infected with the virus, or
• are connected to infected computers on a network system

National Educational Association, November 2001