It was copyright protection, not anti cheat, and I thought it was fun/interesting as well!

It was called FADE <https://kotaku.com/now-this-is-how-copy-protection-should-be...>

It had, another thing is that it used somewhat questionable system for CD key validation, which is stubbed out in this release (https://github.com/BohemiaInteractive/CWR/blob/main/engine/P...).

One thing is 120bit RSA (readily broken with a graphing calculator at the time of release), another thing is the provenance of the RSA implementation code in the original binary.

I think that was arma 2. It also turned the player into a pigeon after a while.