My school had a classroom of BBC Micros which were connected over a primitive network to a "server" which I guess must have had a hard drive for saving files too. I can't take the credit but a school friend worked out how to view the memory of another machine over the network, from which we made the first remote keystroke capture I had ever seen, which got us the teachers' passwords.

Our first hack was born - with their password we could get onto the server and print out the password file (in plain text of course). The teachers started to realise they'd been hacked but I think thought it more likely we'd observed their typing when sat nearby and so changed their passwords. Of course we could just keep watching their passwords being entered at a distance.

I think we were caught in the end red handed with the password file printing out and unable to stop it printing when they came in the room. Luckily back then it was seen as experimentation not criminal!