TO ALL THE PEOPLE GETTING "DISCONNECTED BY HOST"
The only thing you can do is restart your router, if that doesn't solve it, sorry to tell you but you're banned

Did some research, this is confirmed by IW. However it's stupid, why don't they just have an error message when you try to play online saying "You've been banned from the Call of Duty : Modern Warfare 3 Servers"Hmm recently I've been getting into a number of hacked lobbies and getting a lot of XP etc (im not the one hacking or anything) and then suddenly everytime I find a hacked lobby and as soon as I shoot someone it says "Network Connection Lost"... however if I play a normal match it lets me shoot people and doesnt kick me out? so Im wondering maybe Im banned for getting a certain amount of XP per game? Tried resetting the router but doesnt work, advice would be appreciated, thanks.