I'm using "molly-guard" to prevent accidential restarts/shutdowns on the wrong machine.
Works perfectly, but I've just encountered the case where molly-guard is installed, but I could still do a "sudo halt" without it asking me for a hostname. Hm...
[SOLUTION]
This is a know issue (Debian bug #552321), and happens if you call halt/reboot commands from within a GNU-screen session.
In my case, I've simply decided to exclusively start commands like this from outside of screen, so molly-guard can work its magic
