This sounds like a really interesting story, would like to read more on why half life 2 specifically? the game itself was pretty well optimized and ran on really low end hardware even back in the day.
Also there was one "that checked if you were printing a specific string used by a popular benchmark program. If so, then it only drew the string a quarter of the time and merely returned without doing anything the other three quarters of the time".
[1]: https://devblogs.microsoft.com/oldnewthing/20040305-00/?p=40...