What exactly are 'crackers'

You've seen the movies.
The 13 year old nerds who hack into banks, websites, etc, but can an early teen really do so much? Not only that, but how do they know how? Its not exactly rocket science, but its not posted on the net.

I know what they do, but how?
It really facinated me, and I simply want to know more about them

(not asking for a fucking guide here, but im sure you guys get the idea)

>>48
Here's the first one I can find by the way, but that's just grepping through some files so it might be inaccurate:

http://dis.4chan.org/read/prog/1176290300/42

I remember the thread, but I'm not entirely sure I posted that, I'll have to crack the ID to see.