Petya ransomware victims can now unlock infected computers without paying.
An unidentified programmer has produced a tool that exploits shortfalls in the way the malware encrypts a file that allows Windows to start up.
In notes put on code-sharing site Github, he said he had produced the key generator to help his father-in-law unlock his Petya-encrypted computer.
The malware, which started circulating in large numbers in March, demands a ransom of 0.9 bitcoins (£265).
Petya ransomware encryption system cracked - BBC News