I would like to add one history that happened to myself:
When I was an young programmer, I used to lunch sandwiches in my table. Someday I started to see small cockroaches walking over my table. After killing some of them and clear the table for one week, I decided to investigate. When I oppened the keyboard, there were a very big cockroach in inside, and a lot of small ones walking around.
So I realized that my computer was full of bugs - literally.