In the shadowy world of espionage, there is no fool-proof system for preventing the betrayal of an Aldrich Ames, Julius and Ethel Rosenberg, Jonathan Pollard, or, if allegations prove true, Los Alamos scientist Wen Ho Lee, who was fired this month on suspicion of leaking nuclear-warhead research to China.
Such a system would require the technology to read one's thoughts. So it was with a leap of faith this month that NATO - which stared down the Soviet Union during 40 years of the cold war - inducted three former Soviet satellites as new members: Hungary, Poland, and the Czech Republic.
Some NATO officials say the Western alliance's strategic embrace March 12 of former enemies, a decade after the stunning collapse of communism, means, the new members' military and political elites are now privy to NATO's deepest secrets. And though these countries have purged most of their hard-line Communist officials, their historical ties and geographic location make them perhaps more vulnerable to infiltration. Many Warsaw Pact military officers were trained in places like Moscow and Kiev; some brought back wives. Moreover, trade relations then were cozy with nations like Iraq, Iran, and Libya.
"There's still the residue of contacts and relationships between Central Europe and those parts of the world," says one NATO official in Budapest, the Hungarian capital. "If Russia, for example, wished to seize classified NATO material, it might be easier to do it here than, say, in London or Paris."
There have been troubling cases in the past. In Poland, Prime Minister Jozef Oleksy resigned in 1996 amid charges he had been a longtime spy for the Soviet KGB. The case was ultimately dropped for lack of evidence. A second furor erupted in 1997, when a Russian businessman was accused of buying large sections of the Polish economy, as part of an alleged plot by Moscow to somehow jeopardize Warsaw's chances of joining NATO and the European Union.
Just a few weeks ago, the government of the Czech Republic fired the head of its counterintelligence service for reportedly keeping mum about an Iraqi plan to bomb the offices of Radio Free Europe in Prague. The bombing, allegedly organized through the Iraqi embassy, was said to be retribution for beginning a Radio Free Iraq news service last year.
Even longtime NATO member states are not entirely free from embarrassment. Last November, it surfaced that a French major working at NATO headquarters in Brussels had passed to Serbia NATO's plans for military strikes in Kosovo, the southern Serbian province engulfed in civil war.
Not surprisingly, then, when NATO officials speak privately of "hostile" intelligence agencies, they identify three regions - Russia, the Middle East, and the Balkans - as the primary threats.
But there is a second side to this coin, says Tamas Wachsler, a state secretary at the Hungarian Ministry of Defense. "While these countries know us, we also know them and their tactics," he says. "From this standpoint, NATO shouldn't view us as a deficit, but as an asset."
Today, much of what was once secret is easily accessible on the Internet. Still, the most sensitive, unavailable NATO data remain related to its weapons of mass destruction, air-defense system, storage depots of fuel and ammunition, and communication and transportation systems.
DESPITE their new status as "full and equal" partners of NATO - boosting the alliance to 19 members - the Central Europeans will learn NATO secrets in line with the "need to know" principle. Under instructions from the alliance, each newcomer has taken both legal and practical steps in recent months to do what it can to prevent classified material from falling into the wrong hands.
According to NATO specifications, all three established new systems for handling classified material - such as secure telephone lines and storage facilities - and a screening process for those who will have access to such material.
Candidates submit to a rigorous questionnaire and interviews. These probe for potential liabilities - like family, financial, or psychological problems - that may expose the candidate to bribery or blackmail.
"It's like a marriage," said another Western officer in Budapest. "Hopefully, from that first day you have the same level of trust, and it continues to grow ... If the trust and confidence weren't there, they never would have been invited to join."
The three newcomers are quick to recount the misery suffered through the centuries at the hands of foreign invaders. It wasn't long into the post-communist transition that each listed NATO membership as its top foreign-policy and national-security objective.
When it comes time to keep a NATO secret, national pride will be at stake, says Lt. Gen. Lajos Urban, the No. 2 officer in Hungary's armed forces. "We want to be seen as contributing to NATO's strength and trusted as a new military ally," he says.
Another issue is the fate of those Hungarian, Czech, and Polish agents who for years operated covertly in the West. Are they still active, or have they found new employers? Either way, it seems accepted as par for the course.
"You think there aren't American agents in Paris, or French agents in London? Everybody still needs good intelligence," says a third NATO official. "Why should they stop? It's completely natural to want to confirm information you receive. Yes, we're allies and partners, but in other areas we're also competitors."
As NATO neophytes, Hungary, Poland and the Czech Republic will be under pressure to not only to meet the group's expectations, but to perform well enough to enable a second wave of expansion eastward.