1. if you first create the mhfo account, others people are not able to create a new one and so be with the same KSSN'account
2. if a kssn already have an mhfo account, others can't create a new one.
well its like the kssn is already loocked.
3. i dont know
But, do not give your id hangame, if anyone know they can put 3 different password and can block your id account, and if you dont know the kssn you have losted your account.
