Notpron

Notpron (originally stylized as Not Pr0n) is an online puzzle game and internet riddle created in 2004 by German game developer David Münnich. Launched in mid-2004, it describes itself as the "hardest riddle available on the internet" and has developed a reputation for its high level of difficulty.

Regarded as one of the first of the online puzzle game genre, Notpron follows a standard puzzle game layout, where the player is presented with a webpage containing a riddle and must find the answer to the riddle in order to proceed to the next webpage.