It is ‘pwned,’ originated in online games, because the ‘p’ key is right next to the ‘o’ key and it just caught on after a number of people made the mistake.
I get more exposure to this than I really care to, but in this case you benefit since I can kind of answer your question.
It’s “pwn,” as in a mistyping of “own.” Pronounced either “own” or “pawn,” I’ve heard both and there wasn’t a public outcry over mispronunciation. Usage: “I pwned j00,” or simply “pwnd,” mix in a grab-bag of racial epithets, numbers, letters, and stupid as needed.
Re: “roxxors teh boxxors.” I’ve heard two different ideas about it, and there are probably more out there. One is that something “rocks your box” (box = your computer) and the “0rz” was added later. The other was that something “rocks your boxers” (your underwear) and the first word was changed for similarity. Hell if I know which one’s correct.