Here's some of the more important parts of the information, which your buddy Sam kindly and lazily copy/pasted from the official announcement:
Details of Temporary Suspension of Financial Transactions
Transactions to Be Suspended:
- June 4, 2016 (Sat) 00:00 ~ June 7, 2016 (Tue) 06:00
- All financial transactions will be suspended [Banking]
- Internet Banking, Mobile Banking, Phone Banking, ATMs [Card]
- Check cards linked to KEB Hana Bank account : Suspended
- Short-term card loans (cash advance) : Partially suspended
- Long-term card loans: Suspended
- Hana Members services linked to a KEB Hana Bank’s account : Suspended (Reload / Withdraw from ATM / Deposit to My Account / Barcode-based settlement)
- Purchases with a credit card (domestic and overseas)
- Short-term card loan (cash advance)
- Available through other banks’ ATMs only
- File an accident report to the Call Center
- Contact Call Center about irregular checks
[KEB Hana | Details of Temporary Suspension of Financial Transactions]
- Money exchange at Incheon/Gimhae airports
UPDATE: They've now also posted basically the same announcement over on their Facebook page now. Here's the embed but it seems to keep showing a "No longer available" message so just use the link if you're curious. They're answering customer comments in the post's comment feed too.
There's more information at the link so be sure to see the full announcement and of course don't forget to do whatever banking stuff you need beforehand. You can also double-check with the Korean-language announcement. I got an SMS (in Korean) about this about a week or so ago but ignored it thinking it was just spam. Turns out I should pay attention more.
I'll have to remember to pull out some cash myself a few days before. I'm a still a pay-by-cash sort of guy most of the time, which is why I am not too thrilled about Korea going coinless. How about just discounting me the 500won rather than me having to pull out another card or slow-as-hell-loading app just to receive my change? A man can dream.