Nervously, John A. Walker Jr. explained that he had top secrets to sell. “I was the first one who met him,” Solomatin told me. “If I had said no, there is no Walker case. I am proud of this case.” I asked what had convinced him that Walker was not an FBI or Navy plant. “When he showed me the code keys,” Solomatin replied with a smile.

There is a moral to the story. Experts such as David Kahn, author of “The Codebreakers,” believe that U.S. codes, crafted by the National Security Agency in its fortress in Fort Meade, Md., cannot be cracked by other countries, even by ace cryptanalysts using supercomputers. But a John Walker, who headed a spy ring and sold cryptographic secrets to the KGB for nearly 18 years, can turn over the keys to the kingdom.

What secrets does the United States have that other countries are after? They cover a wide range: military, especially nuclear weapons and other sophisticated high-tech systems; U.S. spy satellites that whir overhead for the National Reconnaissance Office; codes that enable the CIA, the military and U.S. diplomats to communicate, and a wide array of intelligence methods, such as how the NSA eavesdrops on the world, gathering communications intelligence and electronic intelligence. Countries trying to steal these secrets often rely on their own spies to collect human intelligence, and–in the age of cyberspies–to hack into vital U.S. databases.

And the spying did not stop with the end of the cold war. Robert Hanssen is only the latest in a long line of intelligence operatives arrested on charges of spying for Moscow.

The West, of course, has in turn penetrated the Soviet Union and Russia. Oleg Penkovsky provided vital data about Soviet missiles until he was caught and executed in 1963. A decade ago Vasili Mitrokhin was spirited into Britain with a vast archive of classified KGB secrets. Dozens of defectors have come over to the CIA both during and after the cold war. Earl Edwin Pitts, one of only two previous FBI agents convicted of spying for Moscow, was turned in by a Russian defector.

Efforts to fortify America’s arsenal of secrets were underway before the Hanssen case became public. Early in January, before leaving office, President Clinton issued presidential directive CI-21, creating a counterintelligence czar to try to centralize the government’s spycatching efforts. One of the czar’s first tasks will be to identify those secrets that the nation absolutely cannot afford to have stolen. Communications intercepts would be high on any such list, along with details of America’s nuclear weaponry. No doubt the list will be classified with some exotic designation far above the now mundane top secret. But it will immediately become a target of every foreign intelligence service in the world–and every potential U.S. mole. (Stealing the list might make a sexy plot device for the next James Bond movie.)

In the wake of the latest spy debacle, former FBI and CIA director William Webster will be looking at ways to tighten security, and may well recommend increased use of lie detectors by the FBI; Hanssen was never polygraphed. The bureau has already put into place checks on employees who use its classified databases. But the outlook is not enpcouraging. As long as there are nations, they will spy on each other. The corollary: intelligence agencies, and the nation’s secrets, remain highly vulnerable to agents who betray their trust.