I hadn’t been at Def Con for more than five minutes before I was mobbed by hackers asking to see my conference badge. I had just left the press registration room at one of the world’s largest hacking conferences, but the attendees lurking outside the door weren’t concerned about my journalistic cred. Instead, they were all trying to solve an elaborate puzzle that implicated every attendee—and as I soon found out, I was one of the few people who could help them solve it.

My press badge looked more or less the same as the other attendees’ badges, except the drawings on the badges were different. When I inserted the batteries that came with my badge and the badge lit up, the LED patterns were inscrutable to me. But to the hackers that had surrounded me, they told a story.

“That green light there is your character,” one of them told me. “The red guy is a goon [Def Con slang for conference support staff]. Now watch what happens when we connect our badges.” He clipped a port on his badge to a port on my own. A few lights flickered to indicate that the badges were interfacing and then he disconnected. He pointed to a few lights on the bottom of his badge that had changed from red to green, suggesting he had made progress in the puzzle. Before I passed my badge to the other hackers I looked at the character on my badge and noticed it had moved. I handed my badge to another attendee. “I have no idea what the hell is going on,” he said as he pondered the flickering lights on our connected badges.

I couldn’t have said it better myself.

At Def Con, attendee badges are never just a token of admission to the conference. Each year’s conference badge is a printed circuit board (PCB), the same type of mini computers you’ll find embedded in most modern electronics. For more than a decade, these circuit boards have served as a ticket to an underground social club whose members are all obsessed with solving the puzzles baked into the badge’s hardware. The stakes of the game are high—the first attendee to crack the puzzle wins an “uber badge” that will grant them free access to Def Con for life. But according to most of the attendees I spoke to, it’s the social aspect of the badges, not the prize, that drives their obsession.