Counterintelligence
Counterintelligence is an activity aimed at protecting an agency's intelligence program from an opposition's intelligence service.[1] It includes gathering information and conducting activities to prevent espionage, sabotage, assassinations, or other intelligence activities conducted by, for, or on behalf of foreign powers, organizations, or persons. Many countries will have multiple organizations focusing on different aspects of counterintelligence, such as domestic, international, and counter-terrorism. Some states will formalize it as part of the police structure, such as the United States Federal Bureau of Investigation (FBI). Others will establish independent bodies, such as the United Kingdom's MI5; others have intelligence and counterintelligence grouped under the same agency, like the Canadian Security Intelligence Service (CSIS) [Wikipedia].
Secret action was taken by a country to prevent another country from discovering its military, industrial, or political secrets [Cambridge Online Dictionary].
Counterintelligence. Wikipedia. Retrieved from: https://en.wikipedia.org/wiki/Counterintelligence
Counterintelligence (2023). Cambridge Online Dictionary. Retrieved from: https://dictionary.cambridge.org/dictionary/english/counterintelligence