Given that they had full access then the OS means nothing at all
As in the previous comment, techs have replacement motherboards and no doubt with a quick download of any onboard cryto firmware they could have just put in a new board with the malware onboard with maybe radio controlled cash payout. EM Shielding means nothing when you can add a handy aerial outside of cage
The security problem here is access to the ATM and the hardware, even if they improved any onboard crypto thieves need only ramraid to see the new generation of atm board.
Personally I would have everything controlled by the back end with seperate remotely controlled hardware for cash dispension but this would just return the thieves to credential capture and again the onus would be on the account holder to prove they were not implicated. Other than moving all the crypto hardware to the bank card then the ATM are always going to be the weakest link
Ultimately whilst there is easy money to be made then expect more of the same until the insurance companies stop buffering the banks
Biting the hand that feeds IT
