Now 65, Montes spied for Cuba for almost two decades while working at the US Defense Intelligence Agency.
She was arrested in September 2001 just 10 days after the 9/11 attacks, with one former Bush administration official describing her as “one of the most damaging spies the United States has ever found”.
Montes pleaded guilty in 2002 to conspiring to commit espionage as part of a plea deal with federal prosecutors and was sentenced to 25 years in prison.
She acknowledged revealing the identities of four undercover US agents to the Cuban authorities and had faced a possible death sentence if convicted. Federal prosecutors at the time said the four agents whose identities she revealed were not harmed.
Prosecutors said Montes handed secrets to Cuba that were so sensitive they could never be revealed in open court, including information about US surveillance of Cuban weapons.
Montes had “compromised everything – virtually everything – that we knew about Cuba and how we operated in Cuba”, according to Michelle Van Cleave, head of counter-intelligence under George W Bush, who spoke at a congressional hearing in 2012 on Cuba’s “global network of terrorism, intelligence and warfare”.
Jim Popkin, author of a new book on Montes’ operations and the investigation that exposed her, previously told The Independent that her spying “really did grave harm to the country”.
“If Ana had been arrested a couple of weeks before she was, and 9/11 hadn’t happened, I think she would be known as one of the more significant spies [ever caught by the US],” he said.
Officials at the time said Montes was believed to have been recruited by Cuban intelligence when she worked in the Freedom of Information office at the Justice Department between 1979 and 1985, and was asked to seek work at an agency that would provide more useful information to Cuba.She began working for the Defense Intelligence Agency starting in 1985, and was considered a top analyst on the Cuban military.
Investigators said that unlike other infamous Cold War spies, Montes appeared to have been motivated by ideology rather than personal gain, and that she was first approached by Cuba after expressing outrage at US actions supporting a right-wing rebel group in Nicaragua.
Montes was released from a federal prison in Fort Worth, Texas on Friday, according to the Federal Bureau of Prisons. She will be placed under court-ordered supervision – including having her internet usage monitored – for five years and is barred from working for government or contacting foreign agents without permission.
Additional reporting by agencies