My story: We used to learn Pascal in my high school programming classes. Each Pascal program ends with an “end” keyword followed by a full stop (“.”), at least if I remember correctly. I wrote a resident program that would monitor the keyboard and screen and when it detected a full stop inserted after the “end” keyword, an animated critter would appear (made of custom characters inserted into the ACII table) and eat the dot, thus making the listing impossible to compile. I didn’t write the viral code, so that it took some social engineering to run the program on my classmate’s account, but boy it was fun when he started complaining to the teacher that he can’t run the source code because of some creature eating his dots :-)