COMSEC, COMmunications SECurity, is the practice of protecting communications, and types of communications, no one of which is classified in any way, but that when aggregated with others can reveal classified information, even highly classified information. An example of this, probably apocryphal but illustrative nonetheless, is the WWI allies’ putative practice of reading the Berlin newspaper society pages to see which German general or generals were in Berlin for the opera. The portions of the Western front for which those generals were responsible could be expected to be quiet for the time being.
It’s also the real world case that, during the runup to the Allies’ WWII D-Day invasion, military radio traffic was steadily increased in areas in Great Britain’s southeastern regions in order to make it appear that a (the) military buildup was occurring there rather than where it actually was occurring, a deliberate use of COMSEC (here in combination with OPSEC, OPerations SECurity) weakness to spoof the Germans.
Now we learn that the People’s Republic of China’s People’s Liberation Army has been floating a fleet of spy balloons across the world, listening to communications across five continents (apparently, the winds aloft don’t blow southerly enough to get balloons reliably over Antarctica or Australia). The balloons are capable of geo-locating the origins of the communications they overhear, also.
But over five continents? The PLA likely is interested in the doings of the nations resident on those continents; however, the US remains a global power with installations all over the globe. It’s a safe bet that the primary target of those spy balloons is us and our doings around the world.
COMSEC. It would be highly useful to the PLA were its balloons, or the PLA back home on receipt of the intercepted transmissions, able to decode the communications. It’s enough, though, for the comms to be tracked back to their origins. Those concentrations then reveal sites worth focusing espionage efforts on, efforts ranging from spy shoes on the ground to focused listening from nearby locations (like, perhaps, farmland near government sites or office space near government buildings) to directed observations from orbit. Those concentrations can, on occasion, overtly expose sites of which the PLA hadn’t yet learned the existence.
This is only part of what President Joe Biden (D) deliberately allowed a PLA spy balloon to do for several days a bit over a week ago.
It’s only part of what the NORAD Commander, General Glen VanHerck, deliberately allowed with his failure of judgment in not recognizing that a spy balloon (which he correctly understood it to be) from an enemy nation was  demonstrating hostile act or hostile intent that would have allowed him to destroy the device after it entered American airspace (not just our ADIZ) over the Aleutian Islands.