My understanding is there are diffrent types.   A broad genralization is the white and black hat hackers.  White hat hackers do things against there own systems that they are responsible for to help strengthen their own security.  Black hat hackers try to go into systems they are not intended to get into to find stuff they are not meant to see or do other things against the proper owners will.  Red hat hackers dabble in Linux (sorry bad joke in reffrence to Red Hat Linux).  I myself like to hack hardware.  I splice stuff around the house into other than inteneded configurations and will naturally grow into the realm of an overclocker as soon as my wallet agrees with my mind.  So in all honesty it's a broad term to cover many people some that are very honest and work only in the forces of light and then there are those that divert more to the dark side.  Let me know if you have any more questions.