pwnz is NOT a typo for ownz
pwnz means "power-ownz" meaning
1)somebody has a foolproof control of
something. and it is really a tighter control than that depicted by ownz. This controled party has
virtually no chance of escape left for him.
Usually used in the hacker subculture when machines becomes controled by a hacker
2)In playing pranks or jokes, when someone is left with no defence.
To sum up, it means "total control" over someone or
something