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)

is pacifico the guy who hijacked 4chan DNS for several days?
I recall 4chan once redirected to some other forum.

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