Users able to bypass the Lock Message

[A Allen]

We have had this problem for a while now, where the remote users (ie. kids) are able to bypass the lock message applied by teachers with complete ease. This is done by pressing "ctrl-alt-del" so it brings up the lock, logoff, shutdown box. The teacher then locks all the computers in the room and the kids are able to just press "esc" to regain full control of their computer.

We've also recently found this is the case for teacher and pupil logons which have very restricted rights, but admin logons work as normal.

AB Tutor themselves can't reproduce the problem, so I wanted to know if anyone else has experienced something similar and come up with a solution?