One Thursday in January 2001, Maksym Igor Popov, a 20-year-old Ukrainian man, walked nervously through the doors of the United States embassy in London. While Popov could have been mistaken for an exchange student applying for a visa, in truth he was a hacker, part of an Eastern European gang that had been raiding US companies and carrying out extortion and fraud. A wave of such attacks was portending a new kind of cold war, between the US and organized criminals in the former Soviet bloc, and Popov, baby-faced and pudgy, with glasses and a crew cut, was about to become the conflict's first defector.

Four months of phone calls and two prior embassy visits had led Popov to this point. Now he met with an FBI assistant legal attaché to present his passport and make final arrangements. A short time later, he plowed through the wintry cold of Grosvenor Square to a hotel room the embassy had secured for him. He opened both his laptop and the hotel minibar and read his email while downing tiny bottles of whiskey until he passed out. The next day, January 19, 2001, Popov and an FBI escort boarded a TWA flight to the US.

Popov was nervous but excited. He'd left behind his parents and everything else familiar to him, but in the US he would be more than a dutiful son and student. Popov was also a wanted man involved in international intrigue, like a character in one of the cyberpunk novels he loved. Now he would reinvent himself by selling his computer security expertise to the government for a decent salary, then transition to an Internet startup and make himself wealthy.

When the plane landed, though, it was clear the arrangement was going to work a little differently. The once-friendly FBI agents threw Popov in an isolation room, then returned an hour later with a federal prosecutor, a defense attorney, and a take-it-or-leave-it offer: Popov was going to be their informant, working all day, every day, to lure his crime partners into an FBI trap. If he refused, he'd go to prison.

Popov was shocked. He'd been played for a durak—a fool. He was placed under 24-hour guard at an FBI safe house in Fair Lakes, Virginia, and instructed to talk to his friends in Russian chat rooms while the bureau recorded everything. But Popov had some tricks of his own. He pretended to cooperate while using Russian colloquialisms to warn his associates that he'd been conscripted into a US government sting. When agents finally got the logs translated three months later, they angrily pulled Popov from his comfortable safe house and threw him in a small county jail to face charges for his past cybercrimes. Popov armored himself in defiance. "Fuck you," he said. "You have no idea what you're dealing with." But he was scared. Prosecutors around the country were lined up to indict him. There seemed no escape from a future of endless jail cells and anonymous American courtrooms.

Except that in a backwater FBI office in Santa Ana, California, an up-and-coming agent named Ernest "E. J." Hilbert saw that the government needed Popov more than anyone knew.