The group has already released complete information about the bank's network and says the next lot of information published will be about the bank's processing operations.

Banco CBR has more than US$800 million in equity and assets of US$7.6 billion and has a reputation for being one of the most stable financial entities in South America.

Maze recently hit a number of big corporates, including technology consulting firm Cognizant and global insurance provider Chubb.

But an additional tool in its armour is that Maze exfiltrates data from its victims and then uses that data to pressure the victim to accede to its ransom demand.

Several other ransomware groups like REvil, DoppelPaymer and Nefilim have also adopted this tactic.

To prove its threat about credit cards is genuine, Maze has put online 240 credit card numbers with expiry dates and card verification codes (CVCs), but without the last four digits.

"Prevention of ransomware becomes even more important with cyber criminals changing tactics to force the hands of companies to pay ransoms," commented Mark Sinclair, ANZ regional director for security firm Watchguard Technlogies.

"A back-up strategy won't get you out of trouble when the bad guys threaten to release your sensitive business data to the world. Prevention indeed becomes the most effective strategy.

"This includes having next-gen firewalls on the network boundary, advanced endpoint protection on servers and notebooks, ongoing user awareness education and multi-factor authentication to stop the use of stolen credentials or weak passwords."