Worst Cases of Espionage in US History

Carney was a U.S. Air Force intelligence specialist who spied for East Germany during the Cold War. Throughout the 1980s, he provided the Stasi, East Germany’s secret police, with a variety of classified information. His espionage activities, which began when he was stationed in West Berlin, significantly compromised U.S. security. The U.S. Air Force Office of Special Investigations grew aware of Carney’s activities after the fall of the Berlin Wall in 1989 led to the declassification of many Stasi records, and apprehended him in 1991. Carney was sentenced to 38 years in prison.

A CIA officer turned KGB mole, Ames was active during the latter half of the Cold War and for several years afterwards. From 1985 until his arrest in 1994, Ames provided the Soviet Union, and then Russia, with classified information that led to the compromise of at least 100 U.S. intelligence operations and the execution of several U.S. assets. His actions are considered among the most damaging in the history of U.S. intelligence.

Ali Mohamed was an Egyptian military officer who became a double agent for the United States and Al-Qaeda. After immigrating to the U.S., Mohamed worked as an FBI informant while secretly assisting Al-Qaeda with strategic planning and training. His activities included involvement in the 1993 World Trade Center bombing and the 1998 U.S. embassy bombings in East Africa. Mohamed’s dual roles weren’t fully understood until after his 1998 arrest, illuminating complexities in counterterrorism efforts.

A former U.S. Army signals analyst, Boone was convicted for espionage-related activities in 1999. Between 1988 to 1991, while stationed in West Germany as the Cold War wound down, Boone sold classified documents to the Soviet Union, including a handbook detailing how the U.S. intended to wage nuclear war. He was arrested in 1998, and subsequently sentenced to 24 years and four months in federal prison.

In 1995, Kota – then president of the Boston Group computer consulting firm – was arrested for involvement in a spy ring that sold highly sensitive defense technology to the KGB from 1985 to 1990. In addition to selling stolen biotech material, Kota also sought to obtain information about mercury cadmium telluride missile detectors, the special coating used to make stealth fighters invisible to radars, and semiconductor components used in infrared missile-tracking systems. According to an FBI affidavit, Kota met with and passed along information to Russian agents in Bermuda, Portugal, Switzerland, Cyprus, and other foreign locations.

Whitworth was a key figure in one of the most damaging espionage rings during the Cold War. A senior radio operator in the U.S. Navy, Whitworth was convicted in 1986 for selling classified information to the Soviet Union. He was part of the infamous “Walker Spy Ring”, led by John Anthony Walker Jr. (see No. 16), which operated for more than a decade. Whitworth’s actions reportedly compromised U.S. codes and put American national security at significant risk. He was sentenced to 365 years in prison for his crimes.

Koecher was a Czechoslovakia-born intelligence officer who became a double agent for the CIA during the Cold War. He infiltrated the CIA in the 1960s and 1970s, becoming the first foreign spy to penetrate the agency at such a high level. Koecher’s espionage activities included transmitting highly classified information to the KGB. His double agent status was discovered in 1984, leading to his arrest and subsequent prisoner exchange between the U.S. and Czechoslovakia.

A prominent Chinese-American businesswoman, Leung was accused of working as a double agent for both the United States and China. She was recruited by the FBI in the 1980s to gather intelligence on China but was later found to have been secretly passing on sensitive information to the Chinese government. The case, discovered in the early 2000s, was considered one of the most damaging spy scandals in recent U.S. history.

Conrad, a non-commissioned officer in the U.S. Army, was accused of selling top-secret NATO defense plans and documents to the Hungarian and Czechoslovakian intelligence services from 1974 to 1988. His actions reportedly compromised U.S. and NATO military operations during the Cold War. Conrad was arrested in 1988 by West German authorities, tried and convicted in Koblenz, and sentenced to life imprisonment and a fine of over $1 million. He died of a heart attack in prison at the age of 50.

John Anthony Walker Jr. was a U.S. Navy officer who sold classified military information to the Soviet Union. His espionage activities, which involved a spy ring including his son and brother, severely compromised U.S. security during the Cold War, allowing the Soviets to decipher over a million encrypted naval messages, allowing the Soviets to greatly improve their naval warfare capabilities. Walker’s ex-wife contacted the authorities about his activities, not realizing at the time that their son was also involved. After Walker and his co-conspirators were arrested and tried, all were sentenced to life in prison except the son, Michael, who received a 25-year sentence. Walker himself died in prison in 2014, a year before he would have been eligible for parole.

Ali was arrested in Bakersfield, California, as the result of a long-term investigation by the FBI and local police departments. In a plea agreement entered several years later, Ali admitted to conspiring to act as an illegal agent on behalf of the Armed Forces Department of the Republic of Yemen since 1987. In his nearly two decades as a Yemeni spy, Ali conspired to export stolen documents and unlicensed U.S. military equipment – such as bulletproof vests, chemical protective suits, and night vision goggles – to Yemen.

Montaperto is a former U.S. defense analyst who was convicted in 2006 of passing classified information to China. After several stalled investigations, the FBI was able to dupe Montaperto into admitting to providing Chinese military attaches with significant amounts of top secret information during a polygraph test for a faux job interview. According to U.S. officials, Montaperto’s activity may have partially resulted in China successfully evading an U.S. eavesdropping operation that had monitored the country’s links to illicit arms sales.

A senior analyst at the U.S. Defense Intelligence Agency, Montes provided classified information to the Cuban Intelligence Directorate over 20 years, which included revealing U.S. military exercises and unmasking four U.S. spies. Montes was convicted of espionage and is serving a 25-year prison sentence.

In 1998, Clark was convicted on a charge of conspiracy to commit espionage and was sentenced to 12 years and seven months in prison. According to a report from the time of his conviction, Clark was recruited into spying through a leftist campus organization at the University of Wisconsin in 1976. Gaining security clearance through his work as a defense contractor, as well as access to additional documents from State Department employees, Clark passed on classified documents to East Germany for a period of at least 10 years.

Hanssen, a former FBI agent, was arrested in 2001 for espionage activities spanning over 20 years. Working as a double agent for the Soviet Union and later Russia, he provided vast amounts of classified information, causing significant damage to U.S. intelligence. Hanssen’s activities resulted in the compromise of numerous U.S. operations, and reportedly led to the exposure and execution of several U.S. agents. His lengthy tenure as a spy is considered one of the most damaging espionage cases in U.S. history.

Mak, a Chinese-born American engineer, was convicted in 2007 for conspiring to export U.S. defense technologies to China. For over two decades, he passed sensitive information related to naval technology – obtained through his work at Power Paragon, a subsidiary of L-3 Technology -to the Chinese government. His activities were part of a broader alleged Chinese espionage effort to gather foreign technologies and information.

A former union activist and member of the Communist Party U.S.A., Stand, along with his wife, Therese Marie Squillacote, and his friend James Clark (see No. 12), spied for the Soviet Union and later Russia for a quarter of a century. Stand’s role was primarily as a recruiter – he brought Clark into the operation – and courier, passing classified information to Soviet handlers in exchange for money. He was tried and convicted, and received a sentence of 17 years and six months.

Born in China, Chung became a naturalized U.S. citizen and held a secret security clearance through his work for Rockwell and Boeing, which he used to pass information related to the U.S. space shuttle and Delta IV rocket programs to China. Chung’s conviction for economic espionage in 2010 and his resulting 16-year sentence was the first conviction under the United States’ Economic Espionage Act of 1996.

Kadish, a U.S. citizen who served as a mechanical engineer at the U.S. Army’s Picatinny Arsenal in New Jersey, was arrested in 2008 for espionage-related activities. He was accused of providing classified military secrets to Israel, including information about nuclear weapons and a modified version of an F-15 fighter jet. Kadish confessed and pleaded guilty in 2009, but was not sentenced to prison, instead receiving a $50,000 fine. His case was notable for highlighting the issue of allied nations engaging in espionage against each other.

Rees was an Italian-American oil engineer who, having allegedly developed communist sympathies in the lead-up to World War II, began passing on oil-related secrets to the Soviet Union in 1942. After becoming, in the opinion of one analyst, the “most important figure in the development of the Russian oil industry between 1945 and 1960,” Rees was recruited by the FBI as a double agent in 1971 and sent to spy on his contacts in the Russian government.

Alvarez is a former Florida International University professor who, along with his wife, Elsa, was arrested in 2006 and charged with spying for the Cuban government. Their activities reportedly spanned nearly three decades, during which they allegedly passed on information about U.S. political, economic, and military affairs. The couple pleaded guilty to the charges, marking a significant event in the history of U.S.-Cuba relations.

Along with his wife, Gwendolyn, Myers – a former State Department official – provided highly sensitive information to the Cuban Intelligence Service for three decades. The actions of Myers, who operated under the codename “Agent 202”, were considered particularly damaging to U.S. interests due to the depth and breadth of the classified information he passed along. He received a life sentence without of parole in 2010.

Lipka was an American who worked as a clerk for the National Security Agency from 1964 to 1967. Responsible for shredding or otherwise destroying documents, Lipka kept many of them and presented himself to the Soviet Embassy in D.C. offering to turn over a diverse array of of them in exchange for money. Lipka’s activities went undetected until the 1990s, when he was arrested and subsequently sentenced to 18 years in prison.

Trofimoff, a U.S. Army Reserve colonel, was convicted in 2001 for spying for the Soviet Union throughout much of the Cold War. Employed as a civilian in the U.S. Army’s intelligence division in Germany, he reportedly passed classified documents to the KGB in the ’70s and ’80s, reportedly motivated by financial gain. His life sentence, handed down in 2001, made him the highest-ranking U.S. military officer ever convicted of espionage.

Larry Wu-Tai Chin was a Chinese-born linguist and CIA employee who was convicted of spying for the People’s Republic of China for more than 30 years, making him one of the most damaging spies in U.S. history. His activities led to significant information leaks about U.S strategies and policies, particularly those related to China. He committed suicide in his prison cell in 1986 before he could be sentenced.