"A specialized group of cybercrimials" have been identified as the source of the world's largest ever bank heist, with anywhere between $300 and $900 million stolen from over 100 banks worldwide, the New York Times reports.  

The investigation began in 2013, when an ATM in Kiev began ominously spewing cash. Further investigation reveals that hackers had been watching internal bank records, by infecting bank employees' computers with malware via email. The download installed a "RAT", or a remote access tool, which acts as a screen grab for all movements on the victim's computer. 

The attack is already being dubbed "one of the largest bank thefts in history".

No banks have yet acknowledged the theft.