By James S. Kunen S. Avery Brown
December 11, 1989 12:00 PM

Cliff Stoll never balances his checkbook anymore. He’s afraid he might find a mistake. The last time the quiet astronomer looked into an accounting discrepancy, it added up to a two-year intrigue whose bottom line was the smashing of an international spy ring.

“I’m the last person in the world to be involved with spies,” says Stoll, 39, who has recounted his unlikely adventure in The Cuckoo’s Egg: Tracking a Spy Through the Maze of Computer Espionage. Indeed, the self-described ex-hippie is much more at home in the counterculture than in counterespionage. “Me? A lefty from Berkeley chasing a spy and getting caught up with spooks from the CIA? I just don’t see myself that way,” he insists. “I’m just this boring, ordinary person.”

Well, not exactly. Stoll has a Ph.D. in astronomy, but it was his expertise with computers that had landed him a job to help design software for Berkeley’s Keck Observatory. And when grant money for the project ran out in August 1986, he was transferred to manage computers at Lawrence Berkeley Laboratories.

On his second day on the job there, his boss asked him to track down a 75-cent shortfall in the computer accounting system. Stoll quickly discovered that someone using the unauthorized password “Hunter” had used a few moments of computer time. He assumed it was a hacker, some computer-expert prankster, among Berkeley’s students. But a few days later Stoll got a message from the National Security Agency that someone using the Lawrence Berkeley computers had tried to hook into an NSA computer system in Fort Meade, Md.

His curiosity aroused, Stoll programmed his computers to monitor and record every keystroke the hacker might make. He soon determined that this electronic burglar was calling in over Tymnet, a worldwide computer communications network, and had programmed a master key that enabled him to unlock and surreptitiously browse through thousands of files at Lawrence Berkeley—and gain access to hundreds of other computer systems. Over the next few weeks, Stoll caught the hacker making forays into computers at the CIA, NSA, several Army missile bases and the North American Air Defense Command. “We were watching a deliberate, methodical attack from someone who knew exactly what he was doing,” says Stoll. “This guy broke into Air Force bases and computers all across the country, and nobody knew it.”

Stoll persisted in the chase and by late November 1986 had enlisted the aid of an FBI agent in Virginia. With the help of Mitre Inc., a Virginia defense contractor whose computer system the hacker was using as a bridge into other systems, Stoll traced his calls and found they were coming from West Germany. By baiting the Lawrence Berkeley computer with phony national-security files, Stoll was ultimately able to lure the hacker into exposing his location. West German authorities then traced his phone number to the city of Hannover, eventually putting one Markus Hess, 25, under surveillance. Hess, who worked as a programmer for a small computer company, was arrested in March 1989; last August he and two other West Germans were indicted for selling military computer passwords, software and other data to the KGB. While the hackers did not tap into top-secret data, Western security experts believe they would have been able to steal sensitive information on military-base activities and electronic communications.

Stoll looks forward to traveling to West Germany to testify against Hess, who is awaiting trial. “I’d love to see him face-to-face, find out who it was that I chased for so long,” he says. But Stoll is a bit apprehensive. Last June, Karl Koch, a West German believed to be part of the spy ring, was found dead in the woods near Hannover, his body burned with gasoline. Authorities say it was suicide, but Stoll is not so sure. “I’m worried as hell about it, and so is my mom,” he says. “She’s afraid someone will go after me.”

Stoll laughs off the notion that he is some kind of hero. “I was just being persistent,” he says. “I feel more like I’ve done a good piece of science.” Nor is he interested in the jobs as a computer-security specialist that the CIA and other agencies have offered him. He’s happy working as an astronomer at Harvard’s Smithsonian Observatory in Cambridge, Mass. He house-sits a sister-in-law’s home there in between commutes to Washington, D.C., where his wife, Martha, 27, is a federal-court law clerk.

Stoll knew he wanted to be an astronomer from the moment he saw his first telescope as a fifth-grader in Buffalo, N.Y., where he grew up as the third of five children of a bartender and a high school teacher. He has pursued that career ever since, pausing only for a one-year post-college detour in 1973, working as a rock band’s roadie, a pinball-machine repairman and a technician for Robert Moog as he developed his music synthesizers.

The only thing Stoll wants to spy on now is the stars. “There’s a whole universe waiting for me out there,” he explains, “a universe that welcomes me, that I can be alone in at night and still feel a part of it all. And it’s a place where there aren’t malicious, evil people breaking into computers.”

—James S. Kunen, S. Avery Brown in Cambridge