In online gaming, a smurf is an experienced player who uses a new account to deceive other players into thinking he's a noob (newbie). The purpose is usually to play against less skilled opponents who will under-estimate the 'smurf'. The expected result is that the smurf will pwn (dominate) his opponents and humiliate them further as they have been now beaten by an apparent noob.
Haha I played company of heroes last night against two level 6 players. I totally smurfed them with my level 1 account. Poor noobs wanted an easy game.