Cicada 3301 is one of the internet's biggest mysteries. It all started in 2012 when a strange image with a challenge was posted online on 4chan, claiming to look for highly intelligent individuals. See:

What followed was a series of puzzles involving cryptography, philosophy, and even obscure books. Nobody knows who created it or why, but theories range from secret societies to government recruitment programs. It’s been over a decade, and the mystery is still unsolved, leaving us to wonder will we ever know the truth behind Cicada 3301? Interestingly, a few people were said they completed the puzzle and were selected but were bound by a contract preventing them from disclosing anything.It’s been over a decade, and the mystery is still unsolved.

https://www.bbc.com/news/technology-25667292 Cicada 3301: I tried the hardest puzzle on the internet and failed spectacularly (Guardian) Cicada 3301: A puzzle for the brightest minds, posted by an unknown, mysterious organization