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)

My personal opinion on this subject is that all media portraying teenage hackers are horribly outdated. Sure, hacking into something in 1980 probably was pretty easy, so even kids with some weeks of computer experience and the necessary malice and criminal intent could do it.

Nowadays, most systems are heavily protected by firewalls, IDS, enhanced kernel functionality etc. so that in most cases, years of practice and extensive knowledge are required. Oh, and thanks to all that research that went into security for the last years, it will also be pretty easy to catch up to you if you ever manage to get into something.