where? some ancient forgotten forum or shareware site?
my method is not that bad, it won't affect the server with anything visible or that you can even experience, it might add 0.1% cpu usage until you unregister the forward, it really doesn't get bad unless all plugins are inefficient in multiple ways and all these small bits add up
the good thing about it is that it waits for key press, if you only detect movement (as in change of coordinates) then on deathrun maps where the players are slowly being pushed to a pit (I'm sure you know what I mean) would not be detected as afk
I was using the same code on my DR mod a couple years back