Last year (1999), encounters with malicious software (malware), computer viruses, worms & Trojan Horse programs resulted in approximately $12.1 billion in damages. Malicious software has no magical powers. It won't cause your monitor to burst into flames, or gnaw through your keyboard and bite off your fingers.
Computer viruses, Trojan Horse programs and Worms are simply computer programs. In order for one of them to do damage, some type of programmatic code has to be run.

In simple terms, the only way malicious software can infect your computer is if you:

• Run an infected program (i.e., .COM or .EXE)
  
• Boot or attempt to boot from an infected floppy
  
• Open an infected Microsoft Office program
  
• Run an infected Visual Basic Script or
  
• Microsoft Jscript, including "invisible" ones embedded in Web pages or HTML formatted e-mail or news group postings messages.

Threats
Understanding the threats is half the battle in defending against malicious software.

Definitions:
Virus: A computer virus is a self-replicating program that can "infect" other programs by modifying them or their environment.
Worm: A computer worm is a self-contained program that is able to spread copies of itself or its segments to other computer systems.
Trojan Horse: A Trojan Horse is a program that does something undocumented that the programmer intended but that some users would not approve of if they knew about it.

Solutions:
How can you defend yourself against malicious software?
First, you should invest in a quality anti-virus program and keep it up to date.
Second, you should never:

• Open files or e-mail attachments from someone you don't know
  
• Open files or e-mail attachments forwarded to you even if they come from someone you know
  
• Open unsolicited or unexpected e-mail attachments until you confirm the sender's intentions
  
• Open a document with macros enabled, period.
  Boot from a floppy unless you personally created it, write-protected it and hide it

Also:

• Backup your computer regularly
  
• Keep your antivirus software up to date
  
• Scan e-mail attachments or downloaded files before you open them.

In the event disaster strikes, don't panic. Time and patience most often cures all.

Computer Humor
A guy went to his mailbox several times before it was even time for the mailman to make his rounds. A watchful (nosey?) neighbor, noticing the repeated trips, asked if the fellow was waiting for a special delivery.
"No," he answered with annoyance. "That stupid computer of mine keeps telling me that I've got mail." Thanks to Alice Gross.