The more serious of this group will spend hours and hours a day scanning the internet for computers that are vulnerable to a security hole. They will then exploit that hole (using some pre-made tool) and use what is known as a 'rootkit' to give them 'root' (or total control) over a computer. This most commonly happens to Linux and Unix computers, although there was a flurry when the Microsoft RPC vulnerability was announced (see slammer worm).
Commonly-used tools include:
Sub7, BioNet, Net-Devil, NetBus, RAT,Optix, Optix Pro.
Pro player : How long have u had the game for?
Newbie 101 : 3 days d00d I so pwn j00 :E
Pro player : k...
Generally meaning one who hacks fairly well and often.
Can be used when someone is of 1337 (leet (elite)) skill in a game or when someone is incredibly lucky and therefore must have cheated or "hacked."
When being called a h4x0r, it is usually taken as a compliment by gamers unless used in the middle of a cuss-filled rant about how that should not happened.