why do you think there is a anti cheat system? ofcourse you can get banned. and the chance of being banned is high if you use public hacks.
when you are are banned: you cant play multiplayer anymore, you can only play private matchs and special ops.
the anti cheat system of cod mw2 is called VAC. VAC bans are permanent. when you are playing a game; vac will scan you to check if you have hacks on. if it detects a hack: you will get a delayed ban that means you get flagged and get banned in a few days/weeks/months.