Stoll omitted some details from the article because the FBI and its German equivalent, the Bundeskriminalamt (BKA), were still investigating the incident when it was written. The astronomer now has a contract with Doubleday for a book about his work.

Stoll said he gives his girlfriend credit for his big break in the case. He said that because she was annoyed by the constant beeping of the electronic pager, she suggested he lay a trap for the hackers.

To entice the hackers to spend more time on the network, Stoll created a Trojan Horse of his own called "SDI Net," which documented fictitious military information. The hackers took the bait and spent more than two hours reading the material.

Three months later, Stoll said, he received a letter from a man in Pittsburgh asking for information about SDI Net. In April, 1987, he turned the letter over to the FBI, who found that the man had connections to Eastern European governments and immediately began an investigation.

In all, Stoll said, the spy ring attempted to break into about 450 different computers and succeeded in gaining access to more than 40 of them--including data systems at the Pentagon, defense contracting firms and U.S. military bases in Germany, Okinawa, California and Virginia.

Stoll said he notified each of the intended victims as soon as the hackers attacked, most of whom quickly shut off the intrusions. In order to keep watching the spies, he continued to allow them access to his own computer at the Lawrence Berkeley Lab.

"To them, it must have looked as though we were the only ones who didn't detect them," he said. "Whereas in reality, we were the only ones who did."