borntobesting: He told me a couple of years ago it was 18.0.0.232
Still is but it's actually 3 years, not 4. You can see archived versions of Flash here going back to 2010. Be warned, though, you need to be very specific about how you change Flash versions.
FWIW, this is the single best reason to dedicate a browser to the game. I use CD and it doesn't update Flash for this very reason. Rock solid perfomance with always smooth meter. Throw Adblock in for ad-free playing.
The version in the Chrome browser I'm using here is 28.0.0.161 and there's no way I could play the game with the way it acts on this browser with that version. Nightmare Central, I won't even try. :-)