hacking
(v)-er(n), see also hack 
-ok a hacker is one who knows inside out of a system, its vulnerabilities its defects etc. he is a curious person, an explorer who doesnt use the vulns and exploits he has found to damage the system, but to only understand it. he is a highly knowledgeable person and doesnt like to talk about his skills or his recent "hacks". a person who keeps telling you that he/she is a hacker, IS NOT.hackers have built the internet. hackers are engineers.
the image which you have of "hackers" has been built up by the media over a period of time. and the media is senseless, as always.
cracker/cracking- not necessarily a hacker but someone who uses his "skills" to damage a system. his intention is to damage. i emphasize on "skills" cause it is not necessary that the skills are acquired. most of the "crackers" are "script kiddies" who download scripts from the net and try to find a vuln system and then pull a stupid lame prank which can be repaired.