A letter supposedly written by a nun possessed by the Devil has been decoded 300 years after it was penned.

Nun's letter decoded

Nun's letter decoded

According to the well-known tale, a nun at a convent in Italy named Sister Maria Crocifissa della Concezione claimed to have been possessed by Satan.

One morning, she woke up covered in ink having penned the letter, which no one has since been able to comprehend.

But now a piece of software on the dark web claims to have unravelled its meaning.

It's said that the letter describes God, Jesus and the Holy Spirit as ''deadweights'', adding that while God believes he can free mortals, ''this system works for no one''.