The Critroni ransomware is selling for around $3,000 and researchers say it is now being used by a range of attackers, some of whom are using the Angler exploit kit to drop a spambot on victims' machines. The spambot then downloads a couple of other payloads, including Critroni. Once on a victim's PC, Critroni encrypts a variety of files, including photos and documents, and then displays a dialogue box that informs the user of the infection and demands a payment in Bitcoins in order to decrypt the files.
"It uses C2 hidden in the Tor network. Previously we haven't seen cryptomalware having C2 in Tor. Only banking trojans," said Fedor Sinitsyn, senior malware analyst at Kaspersky Lab, who has been researching this threat. "Executable code for establishing Tor connection is embedded in the malware's body. Previously the malware of this type, this was usually accomplished with a Tor.exe file. Embedding Tor functions in the malware's body is a more difficult task from the programming point of view, but it has some profits, because it helps to avoid detection, and it is more efficient in general."