'Deadly' double agent Ana Montes who was a US spy for communist Cuba freed from prison after 20 years

• Ana Montes, seen as "one of the most damaging spies" in US history, has been released from prison.
• The former DIA agent was arrested in 2001 after years of sending US secrets to Castro's Cuba.

Ana Montes, who is regarded as "one of the most damaging spies," has been released from a prison in Texas.

Montes, now 65, worked for the US Defense Intelligence Agency, or DIA, as the top analyst on Cuba during the Cold War. Washington knew her as the "Queen of Cuba" for her insights into Fidel Castro's communist regime.

But law-enforcement officers arrested her in 2001 on conspiracy to commit espionage after authorities discovered that she was also a spy for Cuba.

She was later charged with the offense and pleaded guilty, and was handed a 25-year prison sentence. She served 20 of those years and was released on January 6, according to the Federal Bureau of Prisons database.

Solely ideology — not money — motivated Montes' spying, according to the FBI. She disagreed with US foreign policy and was working to undermine it.

When she was working a clerical job at the Department of Justice, Cuban authorities identified her as someone who would be sympathetic to their cause. They approached her and she agreed to work with them.

She then applied for her job at the DIA, and by the time she was in office in 1985, she was a recruited spy for Cuba, the FBI reported.

She was able to pass highly sensitive information over to Cuban authorities through memory alone.

To escape detection, she never removed any information from her work computer. Instead, she memorized classified details and wrote them into her personal computer when she got home. She then put that information on encrypted discs and sent them to the Cuban authorities.

This lasted for 16 years until her arrest.

Speaking in Congress in 2012, Michelle Van Cleave, the head of US Counterintelligence under the Bush administration, described Montes as "one of the most damaging spies the United States has ever found."

"She compromised everything — virtually everything — that we knew about Cuba and how we operated in Cuba and against Cuba," Van Cleave said.

Chris Simmons, a former investigator with the DIA, described Montes as "a very deadly woman, a very dangerous woman," NBC reported. "A lot of spies historically have given up information, but she repeatedly tried to get Americans killed in combat."

Speaking to CBS, Peter Lapp, a former FBI agent and the lead investigator on Montes' case, believes she will now live out her life quietly as a senior. "That part of her life is over. She's done what she's done for them. I can't imagine her risking her liberty," he said.