system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: "Cracking" a game

While reading threads about the new Arkham Asylum fiasco, I kept running across comments of people saying "just torrent it," followed by others saying the game couldn't be cracked yet. Why not?

What exactly happens when someone "cracks" a game? How come some "cracks" are preferable to others and more stable?

EDIT: You guys have been awesome both in explaining and in not being condescending. Thanks so much!
gpt
Some games come with code that makes it hard to run a copy by just possessing the data for it. For instance, it may make you enter a serial number. You copy the CD fine, install it, and it asks you for the number. You don't know it, so the game refuses to work.

Well, somewhere inside the game there is logic like this:

1. Ask user for serial number
2. Perform some operation to check the number. For instance, all digits should sum up to 9.
3. If the answer is right, continue

Cracking is just interfering with this logic. You can modify the code to jump past the verification step. You can make it still ask for the serial number, but accept any number at all. You could flip the logic around so that it accepts only invalid numbers. Etc.

This was the early era of cracking. Then the companies started making things more complicated. The program may be encrypted and self-verifying, so not only you need to break the encryption and make the change, but also find how it checks itself and defeat that as well.

Some are more devious and don't make it obvious that they know something is wrong. Instead the game runs, but breaks something subtly in such a way that the 5th level becomes impossible to finish.

Any kind of protection is breakable, but with enough effort it's possible to make something that requires considerable thought and time to get around, and it's quite possible that if the protection is good enough the game will remain uncracked for months.