Video games are becoming sneakier and sneakier with every passing generation. As copy protection has evolved over the years, games have become able to defend themselves against those who wish to pirate the latest adventure. Consider the case of Nintendo's Super NES masterpiece EarthBound, a game that can tell if you're playing it in ways you're not supposed to play it and then take action accordingly. EarthBound megasite Starmen.net chronicles what happens to your precious saved progress if you have the misfortune of playing a bootleg copy of the game.
EarthBound's programming was full of anti-piracy stuff. It would often check to see if the game was on a cartridge copier or on a pirate cartridge and then it'd do all kinds of stuff.
A subroutine at address $C0A11C is the first line of defense against pirates, being called upon startup. It first checks to make sure that there's only 8 kilobytes of SRAM, the part of memory used to hold saved games. Cartridge copiers have more, so if it detects that, the game displays a screen that says, "It is a serious crime to copy video games."
At $C0281A there's a check to see if $7EB539 is zero. If it isn't, random enemies appear MUCH more often. This was probably an attempt to make the game unenjoyable.
At $C3FDC5 is another checksum routine that goes through $C0A11C-$C0A150. This one is called after Pokey turns off the Devil's Machine. If any data in that range has been changed, the checksum fails, the game deletes all your saved games (seriously) and then it crashes/freezes up. Neat.
This isn't a recent discovery, but I have to admit that I like how EarthBound takes increasingly drastic steps to ruin the bootleg gameplay experience. Most games would stop with the legal warning screen, but we're talking about a game that grows ever more frustratingly difficult if one persists in playing and then — if that isn't enough — actually leads pirate players down the path all the way to the final battle before wiping out all that hard-earned progress in an instant. That's just evil, yet twistedly appropriate.