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Espionage by the Numbers:
A Statistical Overview

Richards J. Heuer, Jr.
Defense Personnel Security Research Center

Katherine Herbig
Northrop Grumman Mission Systems

The typical approach to research on spies has been the case study – either the in-depth study of a single case or a collection of case summaries to provide a somewhat broader view. This article reports on an Espionage Database Project that takes a different approach. Data are tabulated on all American citizens who are known, from publicly available sources, to have betrayed their country during or since the Cold War.

By tabulating and analyzing data on many cases of espionage, it is possible to gain insights on the nature of spies and spying that are not necessarily apparent from the study of individual cases. Findings from the Espionage Database Project are summarized here in three sections: characteristics of the spies, characteristics of the espionage activity, and prevalence among the spies of several behaviors that are commonly associated with security risk. Because this database uses only unclassified information, while most information on espionage is highly classified, the findings should be regarded as suggestive rather than conclusive.

About the Database

The unclassified Espionage Database is maintained by the Defense Personnel Security Research Center (PERSEREC). It has information on cases going back to 1940, but this article is based on the 150 cases of U.S. citizens who committed espionage against the United States since the beginning of the Cold War in the late 1940s. The database is kept current by adding new cases as they occur and information becomes available.

Individuals are included in the unclassified Espionage Database if they were convicted or prosecuted for espionage or attempting to commit espionage, or if clear evidence of espionage is available in the public domain even though they were not prosecuted. This latter category includes people who defected or fled to another country before they were prosecuted, died or committed suicide before they could be prosecuted, plea-bargained for lesser charges, or were given immunity from prosecution in return for providing evidence on others.

Five types of information are coded in the database: biographic information, employment and clearance status, the spy’s motivation, the espionage act itself, and the consequences of the espionage. Included are details of the espionage offenders' personal and professional lives, their access to classified materials, how they became involved in espionage, and how their careers as spies evolved and ended.

A study of espionage based only on unclassified information has unavoidable limitations. The database represents part of a total population of unknown size. We know only those espionage cases where the perpetrator has been arrested or otherwise exposed to the public. We do not know how many spies have not been identified, or how many spies have been identified but not prosecuted.

Which spies are identified and how many spies are identified depend upon the available counterintelligence sources and methods. These sources and methods change over time and may vary depending upon which foreign country is conducting the espionage. Prosecution of identified spies is often handicapped by lack of evidence; unwillingness to expose sensitive sources or methods during prosecution; or political considerations relating to the foreign country involved. These factors also change over time.

This article does not analyze one of the most important questions -- trends in the prevalence of espionage over time. The data are sufficient only to show trends in the prosecution of espionage.

Characteristics of Spies

Reasonably complete information is available on the significant demographic variables for most of the 150 espionage offenders. Some of the older or more obscure cases are not well reported in open sources. Demographic characteristics of the publicly known espionage offenders are as follows. The number of cases for which information is available on each variable is shown at the end of each entry.

Gender: 93% males, 7% females. Information is available for all 150 cases.

Age when Espionage Began: 6% were under 20; 40% were 20 to 29; 27% were 30 to 39; and 27% were 40 or over. There is a significant difference in ages between civilian and military spies. For the civilians, 44% were age 40 or over at the time they began their espionage. For the military, 57% were 20 to 29 years old when they started. Information is available for 147 cases.

Marital Status when Espionage Began: 57% married, 33% single, 10% separated or divorced. Information is available for 141 cases.

Race or Ethnicity: 84% white, 6% black, 5% Hispanic, and 5% other. Information is available for 141 cases.

Sexual Preference: 95% heterosexual, 5% homosexual. Information is available for 116 cases.

Citizenship: 83% born in U.S., 17% naturalized. Most (77%) of the naturalized citizens who became spies were civilians rather than military personnel. Twenty-six percent of all the civilian spies were naturalized citizens as compared with 8% of the military spies. Information is available for 148 cases.

Education: 7% had less than high school; 39% were high school graduates; 20% had some college; 20% were college graduates; 14% had at least some work toward their Masters or PhD. Information is available for 133 cases.

Type of Employment when Espionage Began: 49% uniformed military, 18% government civilian, 24% government contractor, and 9% had already left government service or their job was unrelated to their spying. Information is available for 148 cases.

Rank of Uniformed Military: 19% were E1 to E3; 51% were E4 to E6; 19% were E7 to WO; and 11% Officer. Information is available for 67 cases. 

Characteristics of the Espionage Activity

The following information about the espionage activity is known from open sources. Data on a number of significant variables are available for most of the cases.


Recruitment: Sixty-four percent of the spies took the initiative in volunteering their services to a foreign intelligence service. Fifteen percent were recruited by a friend or family member, most of whom had themselves volunteered, while only 22% were recruited on the initiative of a foreign intelligence service. These percentages differ for different groups. For example, 71% of all military offenders were volunteers, versus 57% for civilians. Seven of the 12 women spies were recruited by a spouse or boyfriend. Information is available for 148 cases.

Motivation: Information on motivation is broken down by categories commonly used when describing espionage offenders, although it is always difficult to know what was really going on in a person’s head. One individual may have more than one motivation, so the following percentages do not add up to 100%.

Money (either need or greed) was a motivating factor in 69% of the cases, and it was apparently the sole motive in 56%. Disgruntlement or revenge toward employer or some other person or situation was a motive in 27%, and ideology a motive in 22%. Ideology includes beliefs and sympathies resulting from cultural affinity (common ethnic or national background). A desire to please a friend or family member was a motivating factor in 17% of cases, many of them cases in which the spy was recruited by the friend or family member. Twelve percent were attracted by what they perceived as the thrills or excitement of becoming a spy, while 4% were drawn by a compelling need to be recognized and feel important. Only 5% were coerced. Thrills or excitement and need for recognition were, in most cases, supporting rather than primary motivations. Information is available for all 150 cases.

Unsuccessful Spies: Thirty-nine offenders (26% of all those who attempted to commit espionage) were unsuccessful. They were arrested before they succeeded in passing classified information to a foreign country. Of the 39 would-be spies who were caught before they could do any damage, 69% were military personnel, mainly young, unmarried, enlisted personnel with no more than a high school education. All were native-born American citizens motivated mainly by the simple idea that selling secrets would be an easy way to get some money. Interestingly, over 60% of the military personnel in this category were in the Navy.

Length of Espionage: Of the 111 spies who succeeded in passing information to a foreign country, 27% were caught in less than one year. Forty-four percent lasted more than one year but less than five, while 29% remained undetected for five years or more.

Security Clearance when Espionage Began: Fifteen percent of the spies held a Top Secret SCI clearance at the time they began committing espionage. Top Secret clearances were held by 35%, Secret by 21%, and Confidential by 3%. Twenty-six percent held no clearance at all. Those with no clearance include accomplices, witting spouses, those who provided classified information obtained during a previous job when they did have a clearance, and those who provided sensitive but unclassified information. Information is available for 141 cases.

Where Espionage Began: Sixty-six percent of espionage cases began in the United States, with a large majority of those on the East Coast. Of the 34% that began outside the United States, 66% began in Western Europe (mainly West Germany) and 20% in Asia or Southeast Asia. Information is available for 146 cases.

Country Receiving Information: During the Cold War, most espionage was conducted by the Soviet Union and associated Communist countries in Eastern Europe. The surprising thing is how many other neutral or allied countries have also been involved in espionage against the United States. American citizens have been arrested for conducting espionage on behalf of South Korea, Taiwan, Philippines, Israel, Netherlands, Greece, Saudi Arabia, Egypt, Iraq, Jordan, Ghana, Liberia, South Africa, El Salvador and Ecuador. Information is based on the 111 cases in which offenders succeeded in passing information.

Espionage Target: Information from the following organizations was compromised, or, in the case of unsuccessful espionage attempts, was intended to be compromised. The number after each organization is the number of offenders who targeted that organization. Navy, 38; Army, 32; Air Force, 22; CIA, 16; Defense contractors, 15; NSA, 7; State, 7; FBI, 4; Marines, 4; DoD civilians, 4; DIA, 2; INS, 1. Six offenders compromised materials from more than one agency and are, therefore counted twice. Information is available for 146 cases.

Payment Received: Although money tops the list of motivations for espionage, it is interesting to see how few spies received significant payments. Most foreign intelligence services are mistrustful of volunteers and are tight with their money, except in the most important cases. Most spies received relatively little, despite the high risk of getting caught and the monumental cost of espionage to the nation. Of the 111 cases in which spies succeeded in passing information to a foreign intelligence service, information on payments is available for 92 cases. Sixty-four of those receive some monetary payment, while 28 are believed to have received no monetary payments. Offenders who received no monetary payment include those who provided information after defecting to the other side, women who helped their husband or boyfriend, some who appeared to have been motivated only by a desire to help the other country, and others who sought some non-monetary quid pro quo such as help for a local business, post-retirement employment in the country that received the information, or release of a spouse from prison.

Of the 64 spies known to have received cash payments, 11% received less than $1,000; 17% received $1,000 to $9,999; 26% received $10,000 to $99,999; 12% received $100,000 to $999,999; while 4% received $1,000,000 or more. It is noteworthy that some of these payments were made as long as 50 years ago, and that the payment figures have not been adjusted for changes in the value of the dollar over the years. They also represent only the amount that the spy is known to have received. After their arrest, spies often try to minimize the amount of money they received in an effort to minimize their crime.

Length of Sentence: The percentages for each initial sentence length are as follows:18% less than 5 years; 20% 5 to 9.9 years; 18% 10 to 19.9 years; 10% 20 to 29.9 years; 7% 30 to 30.9 years; 2% 40 years; 12% life in prison. Sentencing information is available for 127 cases. Twenty cases are known to have had other outcomes such as defection, suicide, or immunity from prosecution.

Date Arrested or Exposed: Five spies were arrested or otherwise publicly exposed during the decade of the 1950s. This increased to 13 in the 1960s and 13 in the 1970s. Arrests and other public exposures mushroomed to 56 in the 1980s and remained at a high level, with 29, in the 1990s. Information is available for all 150 cases.

Large variations in the number of arrests from one time period to another may be determined more by the nature of the counterintelligence sources and tools that are available during a given period than by changes in the prevalence of espionage. The 1980s have been called the Decade of the Spy because of the number of successful spies exposed during that period. However, it was also the decade of the unsuccessful spy. Many young, unmarried military enlisted personnel were caught before they succeeded in selling any secrets. Of the high number of cases in the 1990s, many were successful spies exposed by sources that became available after the end of the Cold War.

Indicators of Security Risk

Past espionage cases can be analyzed to determine the prevalence among spies of behaviors or circumstances often considered indicative of potential security risk. U.S. Government decisions to approve or disapprove security clearances for access to classified information are based on a set of thirteen Adjudicative Guidelines. These guidelines cover behaviors commonly associated with security risk, such as alcohol and drug abuse, criminal behavior, emotional or mental problems, financial problems, and vulnerability to foreign influence.

Behavioral information may be reported in the publicly available sources only if its presence or absence is particularly noteworthy, or if the case is an important one that receives in-depth media coverage. As a result, information on behavioral indicators of potential security risk is available for only a portion of the cases.

Alcohol Abuse: An offender was considered to have engaged in "excessive alcohol use" if he/she was described in one or more open sources as having an alcohol problem, being a heavy drinker, or having been under the influence at the time of first contact with a foreign intelligence service.

Forty offenders reportedly used alcohol to excess. This is 27% of all offenders or 51% of the 79 cases for which information is available about alcohol use. These are minimum figures. It is quite possible that some of those for whom no information is available on alcohol use actually had an alcohol problem.

Drug Abuse: The numbers on illegal drug use are similar to those for excessive alcohol use. Information is available for 76 of the 150 cases. Of those cases for which information is available, 53% of the subjects engaged in illegal drug use while 47% reportedly did not. The current relevance of such statistics on drug use is uncertain, as the prevalence of drug use, especially within the military, has varied greatly over the years.

Spending Inconsistent with Known Income Level: Spies who obtain significant amounts of money may be tempted to spend their illegal income in ways that attract attention to their unexpected or unexplained affluence. To examine this subject, one can look at the 64 cases in which payment was received. In 23 of these cases (36%), the offenders were reported to have demonstrated financial affluence not consistent with their known income. For the 26 cases in which the spy was paid $40,000 or more, unexplained affluence was reported in 20 cases (77%). As usually happens, unfortunately, this information was not known until after the offender was arrested.

Foreign Interests: The national guidelines governing adjudication of security clearances require consideration of any foreign relationships that may make an individual potentially vulnerable to coercion, exploitation, or pressure. This includes foreign attachments such as family ties, other emotional attachments or obligations to foreign persons, and financial, business, or professional interests abroad. There is concern that conflicting loyalties or conflicts of interest can make a person vulnerable to foreign pressure.

A large percentage of offenders had foreign backgrounds or connections. For example:

  • At least 33% had close foreign relatives. In many cases, the relative was a relative of the spouse, not of the offender.

  • At least 44% had emotional attachments to foreign persons such as spouse, fiancée, lover, friend, or relative other than a parent or sibling.

  • At least 16% had foreign financial, business, or professional interests.

  • At least 17% were naturalized citizens

  • At least 7% lived in a foreign country during part of their formative childhood years, and an additional 8% during their entire childhood.

For analytical purposes, offenders with foreign relatives, foreign emotional attachments of various types, and foreign financial, business, or professional interests are combined as a group called offenders with foreign interests. This group includes 76 (51%) of the offenders.

These offenders with foreign interests can be compared with offenders who had no such interests. Those with foreign interests were more likely to have been recruited directly by a foreign service than those without such background or connections (41% versus 32%), and less likely to have volunteered their services to a foreign intelligence service (59% versus 66%). Of the 76 offenders with foreign interests, foreign relatives played a role in recruiting 26% of them.

Offenders with foreign interests were significantly more likely than other offenders to have been motivated by ideology (34% versus 10%). Recall that in this context the term ideology includes a set of beliefs based on common ethnic or national background. On the other hand, they were less likely to have been motivated by money (61% versus 78%).

It is not surprising that 51% of espionage offenders have foreign interests. This does not indicate that Americans with foreign background or connections are less loyal than other Americans. In considering the security risk associated with foreign interests, it is important to distinguish between susceptibility to recruitment and vulnerability to being targeted for recruitment. Foreign interests do not make one more susceptible (less loyal), but they do make one more vulnerable. Americans with foreign interests have valuable language skills and area knowledge. Because of these skills, they are more likely than other Americans to be in positions where they have access to classified information. They are more likely to have contact with foreigners and more likely to feel comfortable dealing with foreigners. They are also more likely to be accessible for assessment and to be targeted for recruitment by foreign intelligence services.




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