I am using a cookie to keep track of the puzzle state in the browser.  By design, I want user to be able to work the puzzle for extended period without posting back to host (thus can work without an internet connection).  User can close a puzzle, then resume it later without posting back to the host since all necessary info is in the cookie.  But this means that user can refresh and essentially "start over" with the puzzle in its initial state.  But now, of course, the user knows all the answers!

I'm thinking that in "contest mode" I will need to postback as user works the puzzle and keep status on the host. 

Thanks for your suggestions.