Intelligent design question: Computer viruses, designed vs. undesigned?

An assistant prof at a Midwestern university writes me to say,

I asked my grandson (freshman in high school) what percentage of computer viruses evolved and what percentage came about by intelligent design. He estimated 50% Darwinian, 50% intelligent design. I asked him to poll his fellow students and teachers to see what their estimate was.

I think a good follow-up question might be what differences there would be between Darwinian computer viruses and intelligently designed computer viruses.

Well, if anyone out there knows, both the prof and I would be interested to hear.