Some had hilarious protections where the game would screw the player if detected
I will never forget that one day one of my high school friends called me after I’d hooked him up with a pirated version of Crysis and yelled into the phone: “WHY IS MY GUN FIRING CHICKENS?! I CAN’T KILL ANYTHING!”
This reminds me of an underrated tool: http://htck.github.io/bayeux/#!/