Over 300 years ago, at the convent of Palma di Montechiaro in Sicily, a nun named Sister Maria Crocifissa Della Concezione claims to have been possessed by the devil.
According to the story, Sister Maria woke up one morning in 1676 covered in ink, having spent the night writing letters.
Maria, who had been at the convent since she was 15, is believed to have been screaming and fainting while writing the notes, which she said the devil dictated to her.
She claimed the possession was part of Lucifer's plan to turn her against God and convince her to serve evil.
The writing featured a bizarre mixture of letters from archaic alphabets and no one was able to decipher the messages.
Today one of the mysterious texts is still intact and, thanks to researchers from the Ludum science centre in Italy, part of it has finally been decoded.
The breakthrough is thanks to a piece of software discovered on the dark web.
"We heard about the software, which we believe is used by intelligence services for codebreaking," Daniele Abate, director of the centre, told The Times.
"We primed the software with ancient Greek, Arabic, the Runic alphabet and Latin to descramble some of the letters and show that it really is devilish."
The letter is said to describe God, Jesus and the Holy Spirit as "dead weights" and states: "God thinks he can free mortals" but "this system works for no one."
It even goes as far as to claim that God was invented by man.
There is also a reference made within the writing to the River Styx, which in Greek mythology is said to separate the realm of the living from the underworld.
It says: "Perhaps now, Styx is certain."
Despite the findings, Daniele doesn't believe Sister Maria was ever possessed by the devil, but instead that she may have suffered "from a condition like schizophrenia".
He explained: "I personally believe that the nun had a good command of languages, which allowed her to invent the code, and may have suffered from a condition like schizophrenia, which made her imagine dialogues with the Devil."