Now Rodriguez has built an Android app that allows his smartphone to mimic those credit card radio communications and exploit flaws in the NFC systems’ firmware. With a wave of his phone, he can exploit a variety of bugs to crash point-of-sale devices, hack them to collect and transmit credit card data, invisibly change the value of transactions, and even lock the devices while displaying a ransomware message. Rodriguez says he can even force at least one brand of ATMs to dispense cash though that “jackpotting” hack only works in combination with additional bugs he says he’s found in the ATMs’ software. He declined to specify or disclose those flaws publicly due to nondisclosure agreements with the ATM vendors.

What is an NFC Chip? - STMicroelectronics