Originally Posted by prmenrs
Something I learned as a student was, "For what purpose do you need this information?" Usually makes them back off.
That's an interesting tactic -- I'll have to try that one.
Something that works for me is silence. After I've told someone once or twice quite nicely that I can't discuss the information, the next series of unanswerable questions are met with a smile and silence. I just smile and stare. It usually winds up with the person actually saying out loud "you can't discuss that information."