Servicesnet, the South Korean Network Blocking List, lists Korean IP Address ranges, along with older ARIN ranges that have been identified as senders of spam. This blocklist includes entire networks, not individual computers.
I.E.C.C.: E-mail from South Korean Networks: We have blocked mail from most South Korean networks. You cannot simply request delisting - this list does not block individual computers or mail-servers, rather it blocks entire networks.
Servicesnet Reports Subnets
Subnet-based Blacklists are used to reject email from entire ranges of IP Addresses, i.e. providers that are hosting companies sending spam, as well as single IP Addresses that may fall in that range of IP Address.