In 2010, the hacker world watched in awe as Barnaby Jack, a New Zealand cybersecurity expert, performed an act straight out of a heist movie: he made two ATMs spit cash on command, live on stage. This dramatic demonstration at the Black Hat cybersecurity conference instantly turned him into a legend. Jack was known as a “white hat” hacker—an ethical type who hunted down system weaknesses to help prevent cybercrime. But in his relentless pursuit of vulnerabilities, he ventured beyond ATMs and into far darker territory...