This term actually comes from a game created hundreds of years ago, even before computers were invented. This game was called, 'chess'. The object of the game was to put the other player in checkmate, meaning, he was unable to move his king anywhere that he would not be threatened by another piece. Also in this game, you have 8 pieces at the front of your army called 'pawns', these were the least useful of all pieces, but that is not to mean they were worthless. If you could defeat the other player by using your pawn to apply check, that was called, and is still called pawned.
Now, back in the early 80's, before warcraft, counterstrike or even the INTERNET, there were ways you could contact other PC's by using a modem. These were called BBS's and allowed you to connect to individual computers acting as severs where games would be so that people could play other people they did not know. Now, when I used to play these games as well as many other people 22+, they used to use and coined the phrase, 'pwned'. Which was slang for pawned. It eventually was taken from just chess and used in other text based games to taunt the loser of a match. It is now commonly wide spread across the world, although the children do not understand its true meaning.
Saying it came from anywhere else is stating you're a poser for the fact you have no knowledge of gaming history and like to think you do so you make things up. Thanks.
Joe pawned/pwned Goerge along with his queen and knight.