Fun fact: Login spoofing like this is why, from Windows NT on, users have had to first enter a security context with Ctrl+Alt+Del.
For those who don't remember, "break" was not an ASCII character but a literal long unmaskable pause in transmission, and couldn't be generated in software or by reading the paper tape punch, nor could it be read on the host side into an input buffer as it wasn't a character.
The sysadmin for my high school computer lab had written a text-mode DOS login screen that would start Windows 3.11 for workgroups after the user logged in. A few of us kids figured out we could just Ctrl+Break out of it and install/play DOOM, Descent 2, etc. He wised up and wrote a trap for the Ctrl+Break sequence, but I discovered the Alt+3 trick and we continued on our merry way. I don't think he ever figured out how we did it.
(We also hid our games inside a directory named Alt+255, which appeared as a space. A single space was not allowed as a directory name, so it felt like magic to us.)