I'm gonna try it now again and see if it still works after a loooong time :P
The tool only works if you got banned a looong time ago. If you cant connecto to online services this means that you've got banned to late. If this is the case your only option to play steam mw3 is to buy it agin on a different account.
You can also try Teknomw3, it is pretty much the same as alterIWNet.