Todays CD keys is pretty long, so Idk how effective the brute-forcer would be, but I think you should give it a shot anyways!
I don't think I can even try those modern activation keys, I think after X wrong attempts the host will prevent you from further attempts.
This theory only applies to older PC games that came with a install key, without online verification
the theory is too old to really investigate the possibilities, as about all of those older install/cd keys are leaked and maintained since 2002 by some incredible
Lamer, he however managed to get it to 1553 records with 18076 cd-keys, the man even released some 200+ game cdkey registry injector, that manages to "pre-install" cdkeys before you install the game, so it won't ever ask for a key when you install those games