Like the word pwn, this is just a variation used to make your sentences l337. Using uber in front tells the recipient that they got extremely pwned instead of just regularly and the zorz is used to intensify the word.
C4ptain_Krunch: Zomg I just took out their entire TEAM!!!
ChUcKNoRRis74: THey alls nub!
C4ptain_Krunch: U all got Uberpwnzorz!!!1