Infinite health hack / god mode

There seems to be a glitch/hack which gives you infinite health.. or maybe you can choose how much health you get. One game there was a guy who got infinite health.. he was running around and knifing everyone. If you shot him all you got was the hitmarker but he didn't die. And there was another match with another guy.. you could kill him but he had at least 2-3 times as much health as everyone else. Has anyone else experienced something like this? I reported these guys and even saved the game in my file share.. but I think they won't get banned anyway. 

EDIT: Uploaded it to youtube http://www.youtube.com/user/HavocGamerzz