The Cold War between East and West is now part of history, but the subject of espionage can still raise the hackles of old adversaries.
For instance, Moscow took a sharp jab at the Western alliance after NATO last week declared two Russian diplomats in Brussels persona not grata and ordered them out.
The Russian mission to NATO headquarters accused some alliance member states of "trying to provoke an international scandal on purpose" in order to sabotage East-West relations.
The dart was apparently aimed at NATO's Eastern European members, who used to be members of the Warsaw Pact. Moscow has accused its former allies of trying to prevent Russia from developing better relations with the West. The Russians have promised a "harsh and decisive" response to last week's expulsions.
The latest row stems from the spying conviction in Tallinn in February of a former top Estonian defense official, Herman Simm. Simm was the man who handled all Estonia's top-secret material from NATO. He was found guilty of spying for Russian intelligence and sentenced to 12 1/2 years in prison.
Western intelligence officials describe the case as the most serious security leak involving NATO since the end of the end of the Cold War.
Some believe Simm delivered information on the U.S. proposal to build a missile-defense system in Poland and the Czech Republic, insofar as Moscow always seemed to know the latest Western thinking on that controversial issue.
But this is only the latest in a long line of spy cases. An Associated Press report dated May 22, 1984 perfectly mirrors the present. It says that two Soviets had been arrested in Brussels and deported for spying.
The report noted that this brought to eight the number of Soviet citizens expelled from Belgium in less than two years. Four Romanians were also expelled during the same period. And it said a total of 27 Soviet citizens had been arrested for spying in the 17 years since NATO moved its headquarters from Paris to Brussels. The total is much higher today.
Some of these spying efforts were crowned with success. For instance, East German intelligence (Stasi) files opened in the 1990s after German reunification show that many of NATO's secrets were well-known to the communist states. They knew the alliance's plan of action in the event of war in Europe, and they had technical details of NATO's latest equipment, including the Pershing-2 midrange missile.
Another success was the East German spymaster Marcus Wolfe, who led the foreign intelligence section of the Stasi. Wolfe developed the concept of the "Romeo agent," in which a male spy would come west and befriend a female worker in politics or defense. He would then use the relationship to extract information.
One of Wolfe's earlier successes was placing one of his agents, Guenter Guillaume, as a close aide to West German Chancellor Willy Brandt. Brandt was forced to step down when the truth came to light.
Of course, the West had its spies too. One notably successful agent was Polish Army Colonel Ryszard Kuklinski, who spied for NATO and the United States from 1972 to 1981. He sent microfilms of some 40,000 documents setting out Soviet tactical plans for Poland and the rest of Europe in the event of war.
Espionage, like everything else, needs to keep pace with modern developments. And an example from Afghanistan shows it is doing just that. The Swedish daily "Dagens Nyheter" carried a report last month saying that Swedish soldiers are being asked for information via the Facebook online networking application.
Swedish defense officials are quoted as saying that in an apparently casual -- but methodical -- way, soldiers are being asked about NATO deployments in Afghanistan. The Swedes say they view this as an intelligence operation against NATO by an unknown country or organization.