In fact dozens of US spies and informants were killed or imprisoned when a secret communications network was exposed doing just that. I wish I bookmarked a better source, it described that the HTML for the portal was reused on every site, so once it was discovered on one site, everyone using it was burned.

Here's one article that alludes to it re: CIA informants in Iran, but I seem to remember China killing US spies and it just not making the news at all

"an analysis by two independent cybersecurity specialists found that the now-defunct covert online communication system that Hosseini used – located by Reuters in an internet archive – may have exposed at least 20 other Iranian spies and potentially hundreds of other informants operating in other countries around the world.

This messaging platform, which operated until 2013, was hidden within rudimentary news and hobby websites where spies could go to connect with the CIA. Reuters confirmed its existence with four former U.S. officials."

https://www.reuters.com/investigates/special-report/usa-spie...