Heavy prison terms, abduction, execution -- the scale of the fate reserved for double agents and other "traitors" depends on the nature of the regime they have crossed and the need to make "examples" of them.
"In authoritarian or totalitarian states it's the strong arm approach: they try to bring back agents considered traitors and they execute them. That has happened to hundreds of Soviet agents," says French historian Remi Kauffer, counter-intelligence specialist and author of "Les maitres de l'espionnage" (Masters of espionage), published last year.
Oleg Penkovsky, a colonel with Soviet military intelligence who passed top secrets on his country's weapons arsenal to the West at the height of the Cuban Missile Crisis, was tried and executed months after his arrest in 1962.
"According to the rumour circulating at the heart of the KGB he was cremated alive and they make a point of telling young recruits this," says Kauffer, for whom "the harshness of the methods is a function of the need to maintain cohesion in the country and in its (intelligence) services."
Then there is the more recent example of Vladimir Vetrov, codenamed "Farewell".
The celebrated KGB mole furnished France in the early 1980s with thousands of documents on Soviet espionage along with the names of some 500 KGB spies or agents in the West. His cover blown, he was executed in 1985.
"Where democratic regimes are concerned things are much less gruesome -- there is a kind of auto-limitation. Public opinion has to be taken into account," says Kauffer.
In cases which are made public the moles are generally tried and given long jail terms.
Such was the fate of American Aldrich Ames. A CIA agent for more than 30 years he began providing documentation to the Soviet Union in the 1980s, an act believed to have cost the lives of dozens of double agents working for Washington.
Ames received the life sentence in 1994.
- State secret -
Other moles have in contrast managed to live to a ripe old age.
They include British "Cambridge Five" spy ring double agent Anthony Blunt. Unmasked in the 1960s after two decades of passing MI5 secrets to the Soviets, the leading art historian - he was curator of the queen's art collection -- was stripped of his knighthood but granted immunity from prosecution after a full confession, while his memoirs were kept a state secret for 25 years after his 1983 death.
"In an Eastern country there would have been a car accident. In this case (Blunt's) they kept the lid on the until 1979, when the scandal broke. Blunt was then identified as a traitor. But he died in his bed," Kauffer noted.
"Today, generally speaking, when a turncoat is identified a warrant is issued for and if he is captured then he is judged and must serve his sentence," observes Alain Rodier, of the French Centre for Intelligence Research.
According to Rodier, "the liquidation of a turncoat, save for some dictatorships such as North Korea, is no longer the order of the day."
Yet the case of Sergei Skripal, the former Russian spy found poisoned last week in a sleepy southern British city has cast that view into some doubt.
Double agent Skripal was handed a 13-year prison sentence in 2006 for passing secrets to the British but four years later was exchanged in a Cold War-style spy swap between Moscow, London and Washington.
London has pointed the finger of suspicion at Moscow, which denies poisoning Skripal.
Some countries do not hide their determination to run to ground those they consider traitors, as illustrated by cases such as that of Mordechai Vanunu.
Israeli secret service agents abducted the former nuclear technician abducted on a Rome street in 1986 after he revealed secrets to a British newspaper concerning Tel Aviv's nuclear programme.
Vanunu was caught in a so-called honeytrap by a female Mossad agent. Taken to Israel and tried he spent more than a decade in solitary confinement.
Although released in 2004, he is banned from meeting with foreign journalists.
© 2018 AFP