In answer to Doug's question...

Sometimes, yes - it is done as a purely malicious act, meant only to cause grief.

However, sometimes it's a juvenile prank. Adolescents (in mentality if not age) doing it because 'it's cool to be a hacker' or some stupidity. Some virii aren't even meant to cause damage - they're stupid little practical jokes that get dangerously out of hand, or were shoddily programmed and have unintended effects.

A small amount weren't even intended to ever see the light of day - someone writing as an exercise and not realizing they've infected themselves, or (and I've talked with someone involved with this type) someone getting pranked when they're on an intranet, not realizing it, and then porting it out of the closed environment into the 'wild'.

There are all types. I'm certain somewhere out there you could even find one or two of the 'multinational terrorist entities' trying to write virii that the FBI is now paranoid about.

M