Full Of It #170 - Cicada 3301 (Patreon)

Dubbed Cicada 3301 by the army of armchair detectives who would try in vain to solve it, it was described as "the most elaborate and mysterious puzzle of the Internet age". Posted anonymously in 2012, there were 2 follow up puzzles (the last of which still hasn't been solved) in order to find recruits of high intellect, especially where codebreaking and cyber security are concerned. There's an excellent video on the matter linked below, should you want an in-depth awareness of the topic before you hit play.

Wiki: https://en.wikipedia.org/wiki/Cicada_3301

Lemmino video: https://www.youtube.com/watch?v=I2O7blSSzpI