Me and my friend have got to round 2500 by using this glitch. It is very simple. To show u proof,go to the leaderboards and keep going down until u find retarded racoon. We did this glitch a couple days ago and they haven't patched it yet! My gamertag is iBassLiineZz. Ok. First,start the game by urself,and get 2500 points,then open the door to the right,where the underground staircase is,then open the next door,and then the stairs. Jump down to the power,turn it on,and get 1000 points. The round that u get 1000 points on,leave the last zombie alive. Make him chase u,while he's alive,go back to the mainframe and go the way where u opened all the doors and stairs at,at the top of the stairs,open the door to the right,then go into the teleporter and sit in the very back of it crouched down,wait for the zombie to come and kill him. Then set ur controller down and watch the levels skip by really fast (except the dog rounds take a minute or 2) and there u go!