MI-80 De Oppresso Liber

Hackers like nothing more than solving complex problems. One of the most difficult contests at DefCon is known as the Mystery Challenge. Teams compete to solve a series of riddles and cryptographic challenges in order to win respect as well as a black badge, granting them DefCon admission for life.

http://blog.wired.com/27bstroke6/2008/08/the-defcon-16-m.html