My older sister worked for Xerox in the mid 90s, and we started to exchange emails which was a new thing for us at the time. She emailed me some EXE attachment, a legit program that her company apparently thought was fine to email around, and the possibilities intrigued me so I wrote a short application (in Turbo Pascal possibly?) for windows that simply displayed a window with a button that said "don't click this button" and if you clicked it, powered off your PC using the normal windows power off stuff. Took about an hour to research and write. I really just wanted to see if she was dumb enough to click it. She did. Then she called me freaking out about what I just did to her PC. Once she saw the humor in it, she forwarded it to all her friends, and in a week, it had been passed around to thousands of people via the forward button.
Not clever at all, not polymorphic, not TSR, not encrypted, did no damage (unless you forgot to save your spreadsheet), but it could have... and it was passed around like herpes at a whorehouse. Those were heady days indeed.