The author of the 'Locker' (or CryptoLocker V) ransomware program has publically apologised to the malware's thousands of victims and released an 'unlock' database containing decryption keys for what appears to be each machine the malware managed to silently infect.
It's a gesture that's not so much rare as completely unheard of - ransomware developers are amongst the most ruthless ever to hit the Internet and the idea that one might try to undo damage on this scale is extraordinary.
The number of victims of Locker is not clear (the .csv file of keys/Bitcoin addresses appears to have has 62,000 entries) but it is known that the program had quietly infected its victims in the months or weeks leading up to 25 May using a booby-trapped version of Minecraft, at which point it activated its encryption payload.
Files targeted included those with extension including .doc, .docx, .xlsx, .ppt, .jpg, raw, .odf, .rtf, .dbf, .odb, and dbf.
Only a tiny percentage of the total number of victims will have paid the ransom, demanded in Bitcoins, but the developer also released the Bitcoin addresses this implies that the scale of this program's rampage could run to ten or twenty times the number of keys.
Symantec has even estimated that the malware author's haul could be as low as a paltry $169 (£110) from a mere 22 victims.
"I am the author of the Locker ransomware and I'm very sorry about that has happened. It was never my intention to release this," announced someone calling themselves 'Poka BrightMinds', in Pastebin message announcing the database's release.
Unfortunately, the unlock process turns out to be a bit more complicated. Anyone who still has the malware on their PC, the unlock command will have been issued automatically on 2 June, after which they will have received the following message through the software itself:
"I'm sorry about the encryption, your files are unlocked for free. Be good to the world and don't forget to smile : )."
However, anyone who manually de-installed the malware using an anti-virus utility will have to use the Locker Unlocker tool released by a researcher which can be downloaded from the Bleeping Computer website. This can also recover Bitcoin payments including for those who have no idea which address to use
Security researchers and analysts expressed huge surprise and bafflement at the malware author's about turn.
"Now this has never happened before!," said Stu Sjouwerman of KnowBe4, a US consultancy that has a track record of helping ransomware victims.
"The author seems to have either made so much money that he's pulling out of this criminal campaign, or has gotten cold feet and is afraid to get caught either by law enforcement or damaged by a local cyber mafia," he said.
"Now, this seems pretty wishy-washy. If you build code like this, you know very well what you are doing. The fact it was built as a 'sleeper' shows months-long careful planning."
It's a valid point. Not everyone who was infected with this program will see the message on how to reverse its effects, nor will everyone who paid a ransom in Bitcoins be aware that it is apparently possible to be refunded. The damage has already been done.