Cicada 3301
Cicada 3301 is the name given to three sets of puzzles posted online under the name "3301" between 2012 and 2014. The first puzzle started on January 4, 2012, on 4chan, and ran for nearly a month.
Source: Wikipedia, Cicada 3301. Text licensed CC BY-SA 4.0. Not endorsed by or affiliated with Wikipedia or the Wikimedia Foundation.