Mr Jack used his knowledge to raise awareness of the weaknesses.
"If the ATM vendors are aware of the weaknesses, they can implement protection mechanisms,'' he told the New Zealand Herald in 2010.
He decided to investigate ATMs because "people see them as this impenetrable device, and no one had really looked at the underlying software".
The New Zealander taught himself the skills needed to become a hacking expert.
Mr Jack was the head of research at cybersecurity firm IOActive.
The company confirmed his death to 3News and said it would post a statement on their website.
Mr Jack was scheduled to speak on August 1 at the Black Hat security conference in Las Vegas. The headline of his talk was, "Implantable Medical Devices: Hacking Humans," according to a synopsis on the Black Hat conference website.
He planned to reveal software that used a common transmitter to scan for and "interrogate" individual medical implants, the website said.
The conference said it will not replace Jack's talk, but instead leave the slot open so people can commemorate his life and work.