The message, in an unusual top secret cable, said that the C.I.A.’s counterintelligence mission center had looked at dozens of cases in the last several years involving foreign informants who had been killed, arrested or most likely compromised. Although brief, the cable laid out the specific number of agents executed by rival intelligence agencies — a closely held detail that counterintelligence officials typically do not share in such cables.

The cable highlighted the struggle the spy agency is having as it works to recruit spies around the world in difficult operating environments. In recent years, adversarial intelligence services in countries such as Russia, China, Iran and Pakistan have been hunting down the C.I.A.’s sources and in some cases turning them into double agents.

Acknowledging that recruiting spies is a high-risk business, the cable raised issues that have plagued the agency in recent years, including poor tradecraft; being too trusting of sources; underestimating foreign intelligence agencies, and moving too quickly to recruit informants while not paying enough attention to potential counterintelligence risks — a problem the cable called placing "mission over security."

The large number of compromised informants in recent years also demonstrated the growing prowess of other countries in employing innovations like biometric scans, facial recognition, artificial intelligence and hacking tools to track the movements of C.I.A. officers in order to discover their sources.

While the C.I.A. has many ways to collect intelligence for its analysts to craft into briefings for policymakers, networks of trusted human informants around the world remain the centerpiece of its efforts, the kind of intelligence that the agency is supposed to be the best in the world at collecting and analyzing.