French researchers reverse-engineered WannaCry ransomware and released decryption tools. Tools can be used to decrypt some PCs that were forcibly encrypted by the ransomware. The prime numbers used to build the crypto keys remain in Windows memory and have not yet been overwritten. The tools carry several caveats: Affected systems must not have been powered down or rebooted. And security experts and law enforcement agencies recommend not paying ransoms, whenever possible, because they directly funds future cybercrime. WanaKiwi can decrypt both Windows XP and Windows 7 systems.”]
Source: https://www.cuinfosecurity.com/wannacry-ransomware-tools-decrypt-for-free-a-9938