The first image of the game, which requires the player to click the door in order to proceed. Subsequent levels increase in difficulty, requiring the player to perform various tasks such as modifying the url, editing the level image and viewing the page source code for clues.
Notpron has a total of 140 levels, ranging from 82 positive levels, 44 negative levels, and 14 Greek levels (Ranging from Alpha to Nu). These three groups of levels do not differ from each other, apart from them being named differently than the others.
Levels consist of finding either a password (known as a UN/PW by the community) or finding a URL to use for the next level. Passwords do not require the user to create an account, but instead will be given to the user once they have found the answer to the riddle. Each solution to each level is very unique, such as decoding ciphers, image editing, musical knowledge, and even remote viewing.
Inspired by a game he played online entitled "This is not Porn", David Münnich created the first five levels in 2004, put them in a folder temporarily called "notpron" and posted it on his website. Soon, thousands of people showed up to play the game and, by then, it was too late to change the name. As of March 2019, only 63 people have completed it out of 19 million visitors since August 2004.
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