On the old BBC micros, I wrote a script that would loop through all possible passwords and try to log into the teachers password. Nothing was stored on computers in those days, so it wasn't such a big thing.
I got busted, had to go to the Principle, and despite explaining that it would have taken approximately 2 years to loop through all possibilities, he still threatened suspension.
On the BBC's Econet system unless a machine was 'protected', any other machine on the network had access to its RAM - including the keyboard buffer. So it was fairly easy to get access to the teacher's password, especially if they always used the same machine and you could make sure in advance to unprotect it!
I got busted, had to go to the Principle, and despite explaining that it would have taken approximately 2 years to loop through all possibilities, he still threatened suspension.