How a Computer Sleuth Traced a Digital Trail

By John Markoff

Copyright © 1995 The New York Times Company

Raleigh, N.C., Feb. 15

It takes a computer hacker to catch one.

And if, as Federal authorities contend, the 31-year-old computer outlaw Kevin D. Mitnick is the person behind a recent spree of break-ins to hundreds of corporate, university and personal computers on the global Internet, his biggestmistake was raising the interest and ire of Tsutomu Shimomura.

Mr. Shimomura, who is 30, is a computational physicist with a reputation as a brilliant cybersleuth in the tightly knit community of programmers and engineers who defend the country's computer networks. And it was Mr. Shimomura who raised the alarm in the Internet world after someone used sophisticated hacking techniques on Christmas Day to remotely break into the computers he keeps in his beach cottage near San Diego and steal thousands of his data files.

Almost from the moment Mr. Shimomura discovered the intrusion, he made it his business to use his own considerable hacking skills to aid the Federal Bureau of Investigation's inquiry into the crime spree. He set up stealth monitoring posts, and each night over the last few weeks, used software of his own devising to track the intruder, who was prowling the Internet. The activity usually began around midafternoon, Eastern time, broke off in the early evening,then resumed shortly after midnight and continued through dawn.

The monitoring by Mr. Shimomura enabled investigators to watch as the intruder commandeered telephone company switching centers, stole computer files from Motorola, Apple Computer and other companies, and copied 20,000 credit-cardaccount numbers from a commercial computer network used by some of the computer world's wealthiest and technically savviest people.

And it was Mr. Shimomura who concluded last Saturday that the intruder was probably Mr. Mitnick, whose whereabouts had been unknown since November 1992, and that he was operating from a cellular phone network in Raleigh, N.C.

On Sunday morning, Mr. Shimomura took a flight from San Jose, Calif., to Raleigh-Durham International Airport. By 3 A.M. Monday, he had helped local telephone company technicians and Federal investigators use cellular-frequency scanners to pinpoint Mr. Mitnick's location: a 12-unit apartment building in the northwest Raleigh suburb of Duraleigh Hills.

Over the next 48 hours, as the F.B.I. sent in a surveillance team, obtained warrants and prepared for an arrest, cellular telephone technicians from Sprint Cellular monitored the electronic activities of the person they believed to be Mr. Mitnick.

The story of the investigation, particularly Mr. Shimomura's role, is a tale of digital detective work in the ethereal world known as cyberspace.

When a Detective Becomes a Victim

On Christmas Day, Tsutomu Shimomura was in San Francisco, preparing to make the four-hour drive to the Sierra Nevada, where he spends most of each winter as a volunteer on the cross-country ski patrol near Lake Tahoe.

But the next day, before he could leave for the mountains, he received an alarming call from his colleagues at the San Diego Supercomputer Center, the federally financed research center that employs him. Someone had broken into hishome computer, which was connected to the center's computer network.

Mr. Shimomura returned to his beach cottage near San Diego, in Del Mar, Calif., where he found that hundreds of software programs and files had been taken electronically from his work station. This was no random ransacking; the information would be useful to anyone interested in breaching the security of computer networks or cellular phone systems.

Taunting messages for Mr. Shimomura were also left in a computer-altered voice on the Supercomputer Center's voice-mail system.

Almost immediately, Mr. Shimomura made two decisions. He was going to trackdown the intruders. And Lake Tahoe would have to wait a while this year.

The Christmas attack exploited a flaw in the Internet's design by fooling a target computer into believing that a message was coming from a trusted source. By masquerading as a familiar computer, an attacker can gain access to protected computer resources and seize control of an otherwise well-defended system. In this case, the attack had been started from a commandeered computer at Loyola University of Chicago.

Though the vandal was deft enough to gain control of Mr. Shimomura's computers, he, she or they had made a clumsy error. One of Mr. Shimomura's machines routinely mailed a copy of several record-keeping files to a safe computer elsewhere on the network -- a fact that the intruder did not notice.

That led to an automatic warning to employees of the Supercomputer Center that an attack was under way. This allowed the center's staff to throw the burglar off the system, and it later allowed Mr. Shimomura to reconstruct the attack.

In computer-security circles, Mr. Shimomura is a respected voice. Over the years, software security tools that he has designed have made him a valuable consultant not only to corporations, but also to the F.B.I., the Air Force and the National Security Agency.

Watching an Attack From a Back Room

The first significant break in the case came on Jan. 28, after Bruce Koball,a computer programmer in Berkeley, Calif., read a newspaper account detailing the attack on Mr. Shimomura's computer.

The day before, Mr. Koball had received a puzzling message from the managers of a commercial on-line service called the Well, in Sausalito, Calif. Mr. Koballis an organizer for a public-policy group called Computers, Freedom and Privacy,and Well officials told him that the group's directory of network files was taking up hundreds of millions of bytes of storage space, far more than the group was authorized to use. That struck him as odd, because the group had made only minimal use of the Well. But as he checked the group's directory on the Well, he quickly realized that someone had broken in and filled it with Mr. Shimomura's stolen files.

Well officials eventually called in Mr. Shimomura, who recruited a colleague from the Supercomputer Center, Andrew Gross, and an independent computer consultant, Julia Menapace. Hidden in a back room at the Well's headquarters in an office building near the Sausalito waterfront, the three experts set up a temporary headquarters, attaching three laptop computers to theWell's internal computer network.

Once Mr. Shimomura had established his monitoring system, the team had an advantage: it could watch the intruder unnoticed.

Though the identity of the attacker or attackers was unknown, within days a profile emerged that seemed increasingly to fit a well-known computer outlaw: Kevin D. Mitnick, who had been convicted in 1989 of stealing software from the Digital Equipment Corporation.

Among the programs found at the Well and at stashes elsewhere on the Internetwas the software that controls the operations of cellular telephones made by Motorola, NEC, Nokia, Novatel, Oki, Qualcomm and other manufacturers. That wouldbe consistent with the kind of information of interest to Mr. Mitnick, who hadfirst made his reputation by hacking into telephone networks.

And the burglar operated with Mr. Mitnick's trademark derring-do. One night, as the investigators watched electronically, the intruder broke into the computer designed to protect Motorola Inc.'s internal network from outside attack, stealing the protective software itself.

Mr. Shimomura's team, aided by Mark Seiden, an expert in computer security,soon discovered that someone had obtained a copy of the credit-card numbers for 20,000 members of Netcom Communications Inc., a service based in San Jose that provides Internet access.

To more easily monitor the invader, the team moved its operation last Thursday to Netcom's network operation center in San Jose.

High-Tech Tools Force an Endgame

Netcom's center proved to be a much better vantage point. To let its customers connect their computer modems to its network with only a local telephone call, Netcom provides thousands of computer dial-in lines in cities across the country. Hacking into the network, the intruder was connecting a computer to various dial-in sites to elude detection. Still, every time the intruder would connect to the Netcom network, Mr. Shimomura was able to capture the computer keystrokes.

Late last week, F.B.I. surveillance agents in Los Angeles were almost certainthat the intruder was operating somewhere in Colorado. Yet calls were also coming into the system from Minneapolis and Raleigh.

The big break came late last Saturday in San Jose, as Mr. Shimomura and Mr.Gross, red-eyed from a 36-hour monitoring session, were eating pizza. Subpoenas issued by Kent Walker, an assistant United States attorney in San Francisco, had begun to yield results from telephone company calling records. And now came data from Mr. Walker that suggested to Mr. Shimomura that calls had been placed to Netcom's dial-in site in Raleigh through a cellular telephone modem.

The calls were moving through a local switching office operated by the GTE Corporation. But GTE's records showed that the calls had looped through a nearbycellular phone switch operated by Sprint. Because of someone's clever manipulation of the network software, the GTE switch thought that the call came from the Sprint switch, and the Sprint switch thought it was from GTE. Neither company had a record identifying the cellular phone.

When Mr. Shimomura called the number in Raleigh, he could hear it looping around endlessly with a "clunk, clunk" sound. He called a Sprint technician in Raleigh and spent five hours comparing Sprint's records with the Netcom log-ins.It was nearly dawn in San Jose when they determined that the calls were being placed from near the Raleigh-Durham airport.

By 1 A.M. Monday, Mr. Shimomura was riding around Raleigh with a second Sprint technician. From the passenger seat, Mr. Shimomura held a cellular-frequency direction-finding antenna and watched a meter display its readings on a laptop computer screen. Within 30 minutes the two had narrowed thesite to the Players Court apartment complex in Duraleigh Hills, three miles from the airport.

At that point, it was time for law-enforcement officials to take over. At 10 P.M. Monday, an F.B.I. surveillance team arrived.

In order to obtain a search warrant it was necessary to determine a precise apartment address. And although Mr. Shimomura had found the apartment complex,pinning down the apartment was difficult because the cellular signals were creating a radio echo from an adjacent building. The F.B.I. team set off with its own gear.

On Tuesday evening, the agents had an address -- Apartment 202 -- and at 8:30P.M. a Federal judge in Raleigh issued the warrant from his home. At 2 A.M. today, F.B.I. agents knocked on the door of Apartment 202.

It took Mr. Mitnick more than five minutes to open the door. When he did, he said he was on the phone with his lawyer. But when an agent took the receiver, the line went dead.