Cicada 3301
November 26th, 2013Via: Telegraph:
For the past two years, a mysterious online organisation has been setting the world’s finest code-breakers a series of seemingly unsolveable problems. But to what end? Welcome to the world of Cicada 3301.
Wikipedia: Cicada 3301
Similar: OTP22: Calling the ‘Beautiful Minds’ of Cryptogon [OTP22 is very active with many unsolved puzzles.]