Though clandestine, some stations have been used by security operatives. On Sept. 22, 2001, the U.S. Defense Intelligence Agency's senior Cuba analyst, Ana Montes, was arrested. She was known to be receiving messages via Cuban numbers stations.
Ana Montes has just been released.
Ana Montes - among the best-known Cold War spies caught by the US - has been released from prison after more than 20 years in custody.
The 65-year-old spent almost two decades spying for Cuba while employed as an analyst at the Defence Intelligence Agency.
After her arrest in 2001, officials said she had almost entirely exposed US intelligence operations on the island. One official said she was among "the most damaging spies" caught by the US.
Michelle Van Cleave, who was head of counter-intelligence under President George W Bush, told Congress in 2012 that Montes had "compromised everything - virtually everything - that we knew about Cuba and how we operated in Cuba. So the Cubans were well aware of everything that we knew about them and could use that to their advantage. In addition, she was able to influence estimates about Cuba in her conversations with colleagues and she also found an opportunity to provide information that she acquired to other powers."
After her arrest, Montes was accused of supplying the identities of four US spies and oceans of classified material. She was handed a 25-year prison sentence, with the sentencing judge accusing her of putting the "nation as a whole" at risk.
However, unlike other high-profile spies caught during the cold war, Montes was motivated by ideology, not personal gain. She agreed to work for Cuban intelligence in part based on her opposition to the Reagan Administration's activities in Latin America.
In particular, a report from the defence department's inspector general found, she is believed to have been angered by US support for the Nicaragua Contras - a right-wing rebel group suspected of committing war crimes and other atrocities in the country.
https://www.bbc.com/news/world-us-canada-64200872