Let's say that someone in the military decides to use the word PANDA as a classified military code word to cover a certain type of activity -- for example, all signals intelligence (see <https://en.wikipedia.org/wiki/Signals_intelligence>). We will abbreviate PANDA as "PX", and if you have a TS (Top Secret, see <https://en.wikipedia.org/wiki/Top_secret>) SCI (Sensitive Compartemented Information, see <https://en.wikipedia.org/wiki/Sensitive_Compartmented_Inform...) clearance and you have been read onto this compartment, then you can be said to have a "TS/SCI/PX" clearance.

Now, PANDA (or PX) covers all signals intelligence. All satellite surveillance of any type. All "bugging" technologies. All interception of digital communications, human or otherwise. Basically, pretty much everything that the NSA does. And a good part of what the CIA does. A TS/SCI/PX clearance is the minimum necessary to work at the NSA, CIA, White House Communications Agency, or pretty much any of the other dozens and dozens of intelligence agencies in the country.

Any compromise of PANDA would mean that hundreds or thousands of classified military projects would be impacted, some of which might be so sensitive that they have to be shut down entirely rather than be associated with a now-compromised keyword. Each of these projects might have to spend thousands or millions of dollars to reclassify their work, and to do what they can to mitigate the damage done. Each project might have hundreds or thousands of personnel who might no longer have jobs, either for the short term or the long term, because of the compromise.

Now, let's assume that some silly person decides to write an article about PANDA, using it as an example of how an SCI code word is used and what it covers, and publishes that in Wikipedia (or Hacker News). And maybe that also gets published on the front page of the Wall Street Journal.

Any time you get a single intelligence agency to run around like a chicken with their head cut off because of some minor compromise, that event probably costs hundreds of thousands if not millions of dollars. Now imagine what it would cost if the code word for the largest SCI compartment was exposed, and all of the intelligence agencies in the country were running around like chickens with their heads cut off. And all of DoD, for that matter.

Do the math.

Frankly, I think just "billions of dollars" might actually be low-balling the numbers somewhat with regards to the upper boundary, but then I'm just guessing -- I have no first hand knowledge of that kind of activity or cost.

But I do know which compartment was affected by the book I saw.