From zdnet.com
South Korea telco KT said on Monday that the temporary nationwide shutdown of its network earlier today was caused by a large-scale distributed denial-of-service (DDoS) attack.
Customers who use the telco’s network were unable to access the internet for around 40 minutes at around 11am on Monday.
Users were unable to use credit cards, trade stocks, or access online apps during that time period. Some large commercial websites were also shut down during the outage.