The iconic image of shadowy undercover agents, risking their life for the cause they believe in has long been a source of fascination.
But modern spying is largely a matter of听collecting vital information from behind a desk using modern technology. Are the days of lone听agents operating behind enemy lines over?
One undercover operative was British Army captain Robert Nairac.
In the early 1970s Captain Nairac operated as a liaison officer for the British Army in Ireland during the Troubles.
To this day his exact movements remain unclear, but it is believed that he gleaned vital intelligence whilst undercover within the IRA.
But concerns started to grow about his behaviour in the field. According to former SAS officer Ken Connor:
鈥淣o one seemed to know who his boss was, and he appeared to have been allowed to get out of control, deciding himself what tasks he would do.鈥
This attitude may have led to Captain Nairac鈥檚听death.
On 14 May 1977, he visited a pub in South Armagh claiming to be a member of the official IRA.
Suspicions of those in the pub were aroused and Nairac was kidnapped after a struggle and taken to a nearby field. There he was brutally tortured and shot. His body has never been found.
Old school spies
Intelligence officers throughout history have trod a fine line behind enemy lines:
Richard Sorge is recognised as the most successful Russian spy operating in Japan during WWII.
Organising a听large spy ring using his job as a journalist for cover, he furnished Stalin with vital information about Nazi plans to invade Russia.
The authorities became suspicious but Sorge was only arrested when a secret note informing his lover of his plan to leave was found in the street.
He was tried and hanged in 1944 but Soviet Russia only acknowledged his efforts in 1964. 
Frederick Joubert Duquesne mounted sabotage operations against the British during the Boer War but was betrayed before his plan took effect.
Staving off a death sentence by selling phoney intelligence, he then escaped using a spoon to dig through castle walls.
Driven on by a hatred for the British, in WWI he infiltrated Field Marshal Kitchener's entourage on a North Sea crossing and signalled a U-boat to sink it, killing Kitchener and much of the crew.
Arrested for the attack in New York, he feigned paralysis and escaped the hospital dressed as a woman.
His career came to an end in WWII when he was arrested for organising the largest spy ring in American history. This time he did not escape.
T E Lawrence became known as "Lawrence of Arabia" after he posed as an Arab to lead a rebellion in the Hejaz against the ruling Turks in 1916.
Making contact with Arab leaders as an intelligence officer in Cairo, he formed an听 alliance of Arab fighters听who opened a second front on the Turks, mining bridges, collecting intelligence and conducting a successful campaign of guerrilla warfare.
During his campaign he was wounded, captured and tortured and听endured the hunger and privations of the desert.
