A really challenging puzzle
You may have encountered this puzzle previously -- it is a great challenge -- a good way to test your web development skills and a nice diversion from coding sessions. The most important outcome is not finding the hidden message -- I will eventually reveal what it is if there is enough interest and people keep working toward a solution -- but explaining how you arrived at it . This exercise also illustrates the futility of trying to hide source code.
Hint: there are several ways to solve the puzzle. If you have seen and solved this before, please don't let the cat out of the bag just yet (there is a clue here).