they use other people's~ lol.
you can simply google it and you'll find a list of them,
but most of them are probably used, especially for popular websites
like netmarble, nexon, pmang etc.

i despise people using other people's kssns though D:<
now, let's hush as kssns aren't allowed to be spoken about here :x~

btw, if the kssn ISN'T YOURS, it's illegal.
a real one doesn't make it legal if you don't own it. if you use it, that makes you the criminal x)
it's just like someone stealing your social security number. i definitely would be mad if
someone stoled mine to register for a game that i can't play since someone already used my kssn ;0~

the only way to get a legal kssn of your own is to be a citizen of south korea.

basically, kssn = korean social security number.