Good article about some of the spy vs spy stuff Trump team has used to catch leakers.
https://www.americanthinker.com/articles/2017/07/trump_and_the_canary_trap_.html
Any “official” who has been leaking should be concerned, and here’s why. One method the Trump administration is likely using to identify these leakers is called “the canary trap,” a term coined by Tom Clancy in his novel Patriot Games. The canary trap is a method for organizations (including many intelligence agencies and private businesses) to determine who is improperly providing information to those not eligible to receive it. They do this by “leaking” certain information, often false, and then following it to see who ends up with it and how they did so.
The method cited in Patriot Games applies to documents. Each copy of a sensitive document is printed with slightly different punctuation, word usage, etc. to make it unique. If a reporter quoted certain parts of the document, that uniqueness would identify the document and the one person who had given it to the reporter. This process can be partly automated now by use of computer synonym generators.
I do, so miss Tom Clancy, may he RIP!