Formerly a senior analyst for the Defense Intelligence Agency (DIA), Ana Belen Montes was convicted in October 2002 of espionage and sentenced to 25 years. Ms. Montes provided various pieces of information to the Cuban Intelligence Service (CIS) including details of wargames held to design contingency plans for a US invasion of Cuba, names and activities of four US agents in Cuba, details of US electronic eavesdropping, and knowledge of US detection of Cuban weapons emplacements.
Ms. Montes would communicate with the CIS by trading floppy diskettes with a Cuban agent. The instructions from her Cuban handlers was encrypted and the key needed to decrypt the codes was transmitted by shortwave radio from Cuba at designated times and frequencies.
In a statement at her sentencing, Ms. Montes said, "...I felt morally obligated to help the island defend itself from our efforts to impose our values and our political system on it." She violated the law and betrayed her colleagues not for material gain, but for idealism.
sources:
http://news.findlaw.com/hdocs/docs/montes/usmontesaff901.pdf
http://www.cicentre.com/Documents/DOC_Montes_1.htm