It is, but people are terrible about it anyway. At a minimum, it is a field day for social engineering attacks because you can learn to speak in the languages / abstractions of that specific organization which automatically leads to trust-building.

can confirm that defense people are terrible about spilling a lot of details in public, but I don’t think I’ve ever heard an actual classified piece of info spoken in public

I once sat at a bar next to a drunk guy who told me he was a Boeing engineer. He proceeded to describe to me how jet engines work, one limitation of common designs, and a way to work around it. I didn’t understand any of it. I got the impression he was very interested in his work and didn’t have people he could discuss this stuff with.

He then told me about a limitation with the SR-71 Blackbird (Apparently the panels of the body expand at high speed, so they have to be designed in a way where they have gaps and are leaky on the ground, until they reach sufficient speed.)

He said solving this problem would be a big deal. Then he wrote the word, “Aurora” on a napkin and immediately crumpled it.

How would you know if the information you heard was classified or not ?

I’d imagine that if you happen to work in the industry, then you would know if what you were hearing was a problem.

From what I’ve read, those with clearances that hear something outside of a secure area are obligated to report it immediately.

It’s even in corporate training to prevent revealing trade secrets accidentally.