I searched the forums for about 20 minutes looking for this:
I remember in Messenger Plus! 3.0, i had a plugin that when i would press a certain combination of keys, it would minimize msn to the tray, set my status to busy, and in order to open msn I would have to type a password i set.
This was my favourite plugin because i could leave msn to gather messages while not having to worry about someone closing msn while i was gone.