In 1990 I also edited a friend's autoexec.bat to launch a quick basic script that would falsely check the disk for viruses and then prompt the user to delete their entire hard disk. Of course pressing "n" would print "y" on the screen and then display a fake progress bar along with a warning to not interrupt the operation in order to avoid disk damage.
I definitely had too much free time at the times. :)
Made me and my friend laugh.
Next session the teacher ask us to sit at the same computer, and after 20mn a guy come to me and ask « Are you pseudo ? »
Turns out that the computers really had viruses and they thought it was me !
They threatened to expel me (more to frighten me I think since they had no proof), and made me the cleaning guy for all the semester.
It gave me an undeserved reputation of the guy who hacked the university computers. And a better sense of caution.