In 2016, tens of thousands of computer-security researchers gathered at the Bally’s Las Vegas for DEF CON, the world’s largest hacker convention. During the four-day conference, attendees witnessed talks and demonstrations on subjects such as how to remotely control an airliner, disarm electronic safe locks, or bypass security on an ATM. But that summer the conference’s organizers wanted to try something sensational, even by the standards of an event where hacking electronic polling stations is ...