“We are looking for highly intelligent individuals”

Eriksson didn’t realise it then, but he was embarking on one of the internet’s most enduring puzzles; a scavenger hunt that has led thousands of competitors across the web, down telephone lines, out to several physical locations around the globe, and into unchartered areas of the “darknet”. So far, the hunt has required a knowledge of number theory, philosophy and classical music. An interest in both cyberpunk literature and the Victorian occult has also come in handy as has an understanding of Mayan numerology.

It has also featured a poem, a tuneless guitar ditty, a femme fatale called “Wind” who may, or may not, exist in real life, and a clue on a lamp post in Hawaii. Only one thing is certain: as it stands, no one is entirely sure what the challenge – known as Cicada 3301 – is all about or who is behind it. Depending on who you listen to, it’s either a mysterious secret society, a statement by a new political think tank, or an arcane recruitment drive by some quasi-military body. Which means, of course, everyone thinks it’s the CIA.

For some, it’s just a fun game, like a more complicated Sudoku; for others, it has become an obsession. Almost two years on, Eriksson is still trying to work out what it means for him. “It is, ultimately, a battle of the brains,” he says. “And I have always had a hard time resisting a challenge.”

On the night of January 5 2012, after reading the “decoy” message from the duck, Eriksson began to tinker with other variables.

Read More | “The internet mystery that has the world baffled” | Chris Bell | The Telegraph