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.

General access to the internet has since been restored for KT users in most areas of the country. 

A KT spokesperson said the telco's network was shut down due to a large-scale DDoS attack. They said that, during the outage, the company's crisis management team was working to quickly restore the network back to normal.

KT is yet to figure out the extent of the damage or who was behind the DDoS attack, the KT spokesperson added.

Federal police and the Ministry of Science and ICT said they were also looking into the matter in collaboration with KT. The ministry did not confirm that the network failure was caused by a DDoS attack, but it said the other major telcos SK Telecom and LG Uplus were not affected.

Despite not being victims of the DDoS attack, users of SK Telecom and LG Uplus' services voiced complaints on social media about these telcos having network failures. Spokespeople for these telcos said the network failures were due to a sudden surge of traffic from KT users shifting onto their services due to KT's internet outage. 

Both SK Telecom and LG Uplus representatives said they would be monitoring the situation closely.

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