Earlier quoted context omitted.
Uhm, as NSA and other agencies are responsible for "secure" internal comm, they have methods for that. Sometimes they get broken, probably, but thats their mission to find out, and sometimes let the enemy continue thinking their breakin is effective. Its the same methods as in 1940, that is, classic intel methods. Security does not just mean strong crypto algorithms. If you find your enemy has found a flaw in openssl…
These are fair points, but I think the GP comment above was referring as much to political economy type espionage. Say, for example, china wants to spy on a military contractor. Unless the NSA is sharing its secure pigeon network with every US defense contractor (and many of them, large and small) some pretty important US national security assets might be in play. So, perhaps not "state secrets" but things like techn…
It could be methods like increasing security for those companies gmail accounts - on the Google internal network and all, closing all normal backdoors on Tesla employee computers, installing NSAs own intrusion detection system on them and such.
And to top it off, feed any Chinese and Russian hackers misinformation through honeypots and "accidents".
In Sweden for example during cold war it was quite popular to install extra instrumentation on jets and provide "just for the soviets" technical documentation - seed confusion and such.