The most dramatic cybersecurity story of 2016 came to a quiet conclusion Friday in an Anchorage courtroom, as three young American computer savants pleaded guilty to masterminding an unprecedented botnet—powered by unsecured internet-of-things devices like security cameras and wireless routers—that unleashed sweeping attacks on key internet services around the globe last fall. What drove them wasn’t anarchist politics or shadowy ties to a nation-state. It was Minecraft.

It was a hard story to miss last year: In France last September, the telecom provider OVH was hit by a distributed denial-of-service (DDoS) attack a hundred times larger than most of its kind. Then, on a Friday afternoon in October 2016, the internet slowed or stopped for nearly the entire eastern United States, as the tech company Dyn, a key part of the internet’s backbone, came under a crippling assault.

As the 2016 US presidential election drew near, fears began to mount that the so-called Mirai botnet might be the work of a nation-state practicing for an attack that would cripple the country as voters went to the polls. The truth, as made clear in that Alaskan courtroom Friday—and unsealed by the Justice Department on Wednesday—was even stranger: The brains behind Mirai were a 21-year-old Rutgers college student from suburban New Jersey and his two college-age friends from outside Pittsburgh and New Orleans. All three—Paras Jha, Josiah White, and Dalton Norman, respectively—admitted their role in creating and launching Mirai into the world.

Originally, prosecutors say, the defendants hadn’t intended to bring down the internet—they had been trying to gain an advantage in the computer game Minecraft.

“They didn’t realize the power they were unleashing,” says FBI supervisory special agent Bill Walton. "This was the Manhattan Project."

Unraveling the whodunit of one of the internet’s biggest security scares of 2016 led the FBI through a strange journey into the underground DDoS market, the modern incarnation of an old neighborhood mafia-protection racket, where the very guys offering to help today might actually be the ones who attacked you yesterday.

Then, once the FBI unraveled the case, they discovered that the perpetrators had already moved onto a new scheme—inventing a business model for online crime no one had ever seen before, and pointing to a new, looming botnet threat on the horizon.

The first rumors that something big was beginning to unfold online came in August 2016. At the time, FBI special agent Elliott Peterson was part of a multinational investigative team trying to zero in on two teens running a DDoS attack-for-hire service known as vDOS. It was a major investigation—or at least it seemed so at the time.

'They didn’t realize the power they were unleashing.' Bill Walton, FBI

VDOS was an advanced botnet: a network of malware-infected, zombie devices that its masters could commandeer to execute DDoS attacks at will. And the teens were using it to run a lucrative version of a then-common scheme in the online gaming world—a so-called booter service, geared toward helping individual gamers attack an opponent while fighting head-to-head, knocking them offline to defeat them. Its tens of thousands of customers could pay small amounts, like $5 to $50, to rent small-scale denial-of-service attacks via an easy-to-use web interface.

Yet as that case proceeded, the investigators and the small community of security engineers who protect against denial-of-service attacks began to hear rumblings about a new botnet, one that eventually made vDOS seem small.

As Peterson and industry colleagues at companies like Cloudflare, Akamai, Flashpoint, Google, and Palo Alto Networks began to study the new malware, they realized they were looking at something entirely different from what they'd battled in the past. Whereas the vDOS botnet they’d been chasing was a variant of an older IoT zombie army—a 2014 botnet known as Qbot—this new botnet appeared to have been written from the ground up.