In high school I found there was an whitelist of executable names, as long as I named the file firefox.exe it would be allowed to run. For senior prank I creat

In high school I found there was an whitelist of executable names, as long as I named the file firefox.exe it would be allowed to run. For senior prank I created small Autohotkey executables that would swap what some keyboard keys would do (e.g. 'm' with 'n'). Then I booted the lab computers with a Linux live CD, and copied the executables into the global start folder (a different executable for each computer). When students came in that day to finish their homework in the morning at the last minute, they were quite annoyed, but some found it funny. One clever student figured out that killing the firefox.exe process fixed it (until the next login). I didn't get in any trouble (senior prank was semi-sanctioned), but they did need me to clean it up the next day.