It's actually not that complicated. Most headless browser drivers have some global JavaScript functions in the `window` namespace that immediately identify them

It's actually not that complicated. Most headless browser drivers have some global JavaScript functions in the `window` namespace that immediately identify themselves. I once ran into a piece of code from the scammy advertising world that tried to redirect users to a phishing site. They cleverly tried to hide themselves from the automated quality checks some ad networks do, by checking for these functions and appearing benign if they saw them. One of the checks even created an exception and then inspected the stack trace for certain flags that apparently are only there on some type of headless browser. Clever!