Cracks and codes for software are entirely different things from website logins.
Most software codes are self-authenticating, so that the software knows if the code is correct if all the numbers follow a certain rule (for example, the next 2 digits after a 5 must be either 3 or 7) and once these rules are known, you can make key generators to generate number strings that follow these rules.
Cracks fool the program into believing that it is a registered copy of the software, through many different means.
As far as I know, website logins require a password, usually defined by the webmaster. There's no short way around this, so you'd have to try every combination of numbers/letters/spaces/symbols etc. to guess the password. And since many systems lock you out after a few guesses, it'd be futile.
Even if you could intercept this password, it's essentially impossible (given today's technology) to decrypt the information, unless you have the decryption code.