Inviting friends bonus

As you know you don't receive any bonus if your "friend" have the same ip.. i was wondering when did they check the ip ? is it when the called "friend" 1st open the invitation and register or when he reaches level 7 ? or they detect it all the way ?
please if you don't know don't spam the post

My friend do it with the same ip and he don't get anything.

many people do that themselves, but if you want on internet are a lot of programs to change your IP ;)