Well, I found this totally hilarious. Thanks to Zappykins to show me one of those. I later look it up on internet and found this.

The Michael Jackson thing is hilarious

Hire ninjas.. /thread

Get an anti-piracy software that scares the s*** out of people. I remember how the PS2's red screen of death scared me.

i think the more subtle ones are the best. operation flashpoint is clever. but earthbound deleting itself before the end is awesome.

If they can detect so easily that you are running a pirated copy of the game, can't they just stop you from reaching the main menu instead, and show a message saying "Error: pirated copy"?

Maybe. But since your game is being pirated, you might as well have fun with the people who do so. I mean, the Earthbound thing is purely brilliant.

Then pirates would get pissed off and make it their mission to find the anti pirate code and deleate it. All of these ways are subtle enough that the guy making the copy will think it works fine or not think it's worth it to find the code.

Well, they wanted to hack the game in first place. Let them lose a large amount of time is epic. I can imagine that many people have done twice EarthBound, finally contacted the customer service to be told -> "well, I see that your problem lies in your moral sense, to fix the issue... buy a copy." XD

And if they find pleasure in the game, they will probably buy it.

would be awesome if every enemy in a pirated copy of the game would turn invisible, then reveal themselves as ninjas after they've killed the player.

There's a Spanish game from the 80's, "La Abadía del Crimen" with one of those anti-pirate things.

If the game finds  that you are playing a pirated copy, it changes the music in a certain scene and starts to call you pirata (pirate).

http://www.youtube.com/watch?v=gVH85XUqIeM

(original min 1:45, pirated copy 2:50)