My school's computer lab ran Windows 3.1 for Workgroups on top of DOS. The network login prompt was in DOS. There were some hackers in upper grades who had installed games like DOOM, Descent, Duke Nukem 3D, etc. in a folder named Alt+255 on many of these computers, which looked like a space in DOS but was invisible to Windows Explorer.

The lab manager found out about our Ctrl+Break hack and put in an event listener/handler for that keycode in the DOS login program. So I spent several hours trying other key combinations and eventually figured out that Alt+3 sent an ASCII character that had an effect that was equivalent to Ctrl+Break in DOS -- and we were back in business.