Cicada 3301 is a nickname given to a group that has been anonymously publishing a series of puzzles, ostensibly to recruit an elite group of codebreakers and cryptography experts for an unknown purpose, since 2012. The clues have spanned many different communication media including internet, telephone, original music, bootable CDs, digital images (steganography), physical paper signs, and an encrypted book entitled Liber Primus. Physical clues have been found in 15 US cities and 8 foreign countries. A PGP signature was established to identify authentic transmissions.

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Some believe the Cicada group to be a cult, a secret society, a shadowy government agency, or a hacker collective, but their true identity remains unknown.

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Source: Wikipedia