What is the specific name for this counter-espionage technique?

Factual Questions
1

I am positive there is a specific name for this type of counter-espionage technique meant to reveal the source of an information leak - I was reading about it on Wikipedia a few days ago. But now I can’t remember what it’s called.

Basically, it’s very simple. Let’s say you have four guys working for you, and you think that one of them is leaking information. So you give them four different versions of the same piece of information. Then when the info is leaked, you find out which one did it.

What is this called? I KNOW there is a specific name for this.

2

It’s a Barium Meal Test, aka Canary Trap.

3

Bingo. Thanks. I knew it had some weirdo name like that.

4

You’re welcome. I only knew this because just a couple of weeks ago I was reading about it but couldn’t just now remember where or why. So I just googled “espionage leak different versions” and a Wikipedia link came up that showed I had clicked it before. Then I remembered: I had watched Patriot Games and so looked up the movie and the novel, and that led me to the Canary Trap page.