Just wanted to Share the Last answer from Boom
Yes, it apply to Korea stock as well. Actually, all stocks and cash kept by BOOM on behalf of clients, they have to be in the segregated Trust account, if the client maintain a Cash account with us.
In case of Margin account, the margin agreement allow us to re-pledge client's securities as collateral with other financial institution.
So the risk lies in trusting those stuff and in the worst Case you have to travel to China/Korea and Fight on you own