How to counter defense missile system

we all know about these new defense system which take down missile before they hit the target there are not perfect yet but in future who knows their are only two to three possible way to counter  these system and make them useless 1st is MIRV one missile carry many small warhead to improve its chances and another is with new small rocket or with old wings missile change its direction at high speed and the last is to hack the system or to make it think the target is somewhere else.