An anonymous reader writes: The author of the original Petya ransomware -- a person/group going by the name of Janus Cybercrime Solutions -- has released the master decryption key of all past Petya versions. This key can decrypt all ransomware families part of the Petya family except NotPetya, which isn't the work of Janus, but is believed to be the work of a nation-state actor that targeted Ukraine. Most (original) Petya campaigns happened in 2016, and very few campaigns have been active this year. Users that had their files locked have wiped drives or paid the ransom many months before. The key will only help those victims who cloned their drives and saved a copy of the encrypted data. Experts believe that Janus released Petya's decryption key as a result of the recent NotPetya outbreak, and he might have decided to shut down his operation to avoid further scrutiny, or being accused of launching NotPetya.