First, let's get our facts straight. An intelligence officer is not a spy. A spy is a person who, for whatever reason, works covertly against his own country for the benefit of another country.
For example, the CIA's own Robert Hanssen was an intelligence officer until he started to work for the Soviets, at which point he became a spy. Here at A Secret Eye (Super Spy Me), we tend to refer to them all as spooks. Look around you at people you know, or even complete strangers, and ask yourself this question : “Which of them could be a spy for some other company-religion-ideology-political party-socially militant group?”
That guy sitting next to you at a political meeting could be from the opposition, trying to find out what your party's up to. An ultra orthodox Rabbi in the Israeli government may be communicating strategic secrets to a more liberal family member. That quiet lady in accounting could be carrying home a memory stick containing details of your company's strategies.
If you can come up with a suspect, I'm sorry to say you may very well be wrong. Spies naturally don't want to be found and they act accordingly. Let's say an individual has been approached by the opposition and has become a spy. Either he's able to just go on as if nothing had changed, or he's going to exploit - and/or hide behind - his strengths and weaknesses.
A talkative person who might accidentally spill the beans would become more of a listener. A flamboyant personality might want to act a bit more reserved. In doing so they're adopting a different persona, making themselves not unlike everyone else who's playing a role socially just to get along, or coming down with something, or going through a life event. In short : everybody is “acting” naturally.
But what about the pros? Those people who live false lives in the war of shadows for high stakes and usually come under the scrutiny, not from ordinary folks like you and me, but of other pros trained at weeding out spies. Why do they do it?
H. Keith Melton in his excellent Ultimate Spy gives us the acronym MICE to cover most of it : Money, Ideology, Compromise, Ego.
Opposing intel services take a close look at the finances of a desirable prospect, just in case his financial situation is so bad that he could be turned for money. Intel services also scrutinize their own personnel’s expenses. If a person who makes $80,000 a year suddenly buys a sixty-foot yacht and a big house in Martha's Vineyard, he or she may be selling secrets.
John Anthony Walker's very damaging spying activities were motivated by money.
That's the category where we find most of the infamous Cambridge Five. The attraction that communism had on them in their college days later translated into an intelligence disaster for the United Kingdom and cost it the confidence of allied secret services.
Ideology was also the reason for Julius and Ethel Rosenberg's spying for the Soviets.
Compromise / Coertion
Do you have a secret? Newspapers keep digging up dirt on stars and politicians with deceptive ease. Just imagine what a an opposing intel service can dig up on just about anybody. The threat of seeing its foibles exposed is then used to blackmail the target. We find in this category the famous Honeypot, a technique to recruit spies by compromising them romantically or sexually. In the days of the Soviet Union, agents were trained in the art of seduction for just that purpose. That's how the opposition entrapped Clayton J. Lonetree, the first ever Marine to be convicted of espionage, and also a French diplomat, Bernard Boursicot, the inspiration for “M. Butterfly”.
The GDR's Stasi was very successful at coertion, sometimes literally holding whole families hostage to control an unwilling asset.
Do yourself a favour and see The Lives of Others, an excellent film about Stasi blackmail and coertion in the GDR.
An individual who has not been given the promotions he felt he deserved might harbor bad feelings about his employers, enough to exact revenge by turning on them just to prove his superiority to himself. A honeypot operation can be performed to flatter the ego of, and ultimately turn, someone who has issues in that domain.
In the case of Aldrich Ames, it seems that he felt so superior to his peers that he didn't even try to hide his illegitimate income. This flies in the face of conventional wisdom for anyone who has an illicit source of income, and very much more so when the subject is a career intelligence professional.
But of course nothing, especially in the shadowy world of intelligence, is that simple. Robert Phillip Hanssen was a hit on three of the four categories. Apparently, ideology was not his strong suite. Some sources also create a whole new category for sex-related methods of recruitment, so that MICE becomes SMICE.
As for Fritz Joubert Duquesne, his motivation was pure hatred for the British.
And, of course, some just do it for kicks.
H. Keith Melton (2009), Ultimate Spy, Inside the Secret World of Espionage, DK, ISBN 978-0-7566-5576-1 http://en.wikipedia.org/wiki/M._Butterflyhttp://en.wikipedia.org/wiki/Agent_handling http://en.wikipedia.org/wiki/Motives_for_spying http://en.wikipedia.org/wiki/Clandestine_HUMINT_asset_recruiting#Love.2C_honeypots_and_recruitment http://en.wikipedia.org/wiki/Clayton_J._Lonetree http://en.wikipedia.org/wiki/John_Anthony_Walker#Spy_ring http://en.wikipedia.org/wiki/Fritz_Joubert_Duquesne