For everything technology gave modern espionage, it took something we are still trying to replace.
The KGB used to mark suspected
@CIA officers in Moscow with spy dust, a chemical tracking compound that followed them through the city. Today, that dust is digital, the metadata trail we all generate by carrying a phone, swiping a card, or walking past a camera.
Running a CIA source under this "ubiquitous technical surveillance" and "digital dust" asks something different of intelligence officers.
Yet human nature still drives every operation. When it gets harder to sit across from a source and read them in person, it gets harder to tell a double agent from the real thing.
This is why the answer is still human. CIA needs to hire the best, train them hard, and let them take risks.