After REvil attacked Kaseya, the FBI managed to exfiltrate the master key to decrypt all of Kaseya’s customers’ systems… But they withheld the key for 3 weeks, until REvil disappeared, then they finally handed the key over to Kaseya.
Thousands of affected businesses had spent millions in the meantime trying to recover their systems or pay the ransom for an individual key. Talk about being irresponsible.
The FBI had managed to infiltrate REvil and didn’t want to give the game away, so they sat on the keys and watched thousands of businesses struggle, because they were considering an attack on REvil, which never took place.
(German language article on heise.de, the original story was in the WaPo, but I don’t have a sub there to get to the article.)
Kaseya-Attacke: FBI hielt wochenlang Generalschlüssel zurück | heise online