Espionage Files: The Most Dangerous Spy You’ve Never Heard Of

Programming note: Explore untold stories of American spies: CNN Original Series “Declassified” airs Sundays at 10 p.m. ET/PT only on CNN.

(CNN)She put American combat troops in harm’s way, betrayed her own people and handed over so many secrets that experts say the U.S. may never know the full extent of the damage.

Ana Montes was the Queen of Cuba, an American who from 1985 to the September 11, 2001 attacks handed over U.S. military secrets to Havana while working as a top analyst for the Pentagon’s Defense Intelligence Agency.

But despite her crimes, Montes remains largely unknown.

You might not think Cuba could do much harm to a superpower like the U.S., said retired DIA official Chris Simmons, appearing on CNN’s “Declassified.”

But you’d be wrong.

The threat increases, he said, when Havana goes on to sell those U.S. military secrets to Montes’ anger about U.S. foreign policy complicated her relationships and drew the attention of Cubans who enticed her to turn her back on friends, family and her own country.

Montes’ anger about U.S. foreign policy complicated her relationships and drew the attention of Cubans who enticed her to turn her back on friends, family and her own country.

The fascinating spycraft that surfaced from her case offers a rare glimpse into the invisible world of espionage, where some experts believe there could be as many as 100,000 foreign agents working inside the U.S.

Read the Remainder at CNN