Ahh the beeb.. great memories.
We had dozens of them at the secondary school i went to, one day we made a fake boot screen that looked identical to the normal one you got when you switched on a bbc micro and it went to basic.
This one of ours though logged all the text so people were putting in there *i am .... login and password. Our program logged you in as normal but secretly stored the login info in a file on another network account.
We got practically the whole school with this over time, including the admin account who was a computing teacher. Once he figured out this was going on he did a ctrl-break before logging in.