Linux, the operating system for a vast number of computers, internet servers, and other devices all over the world, had a secret backdoor built into it. Andres Freund, a Microsoft programmer, found it and alerted the world to the insidious vulnerability. The World’s Carolyn Beeler talks with Andy Greenberg, a senior writer at Wired, about the vulnerability, how Freund found it, and the trail of clues that point to who might have been responsible for placing the backdoor into the code.