Personal information of 250 OK Savings Bank customers was confirmed as leaked due to abnormal access to the bank’s website. The leaked data included not only names and dates of birth but also financial transaction information such as account numbers, annual income and loan amounts.

OK Savings Bank said on Wednesday that a detailed investigation carried out with 2 external security monitoring firms confirmed the leak of personal data of 250 customers who used the website’s loan application service.

The leaked items were loan application-related information, including name, date of birth, mobile phone number, account number, address, email, workplace name, business registration number, annual income and loan amount.

The incident was linked to abnormal access attempts that occurred from 8:44 p.m. on Oct. 11 to 2:14 a.m. on Oct. 12. OK Savings Bank said it detected signs of unusual access around 10 a.m. on Oct. 12 and deployed an emergency authorization verification logic update at 11:35 a.m. the same day to block suspected hacking IP addresses and access routes.

It then brought in 2 external security monitoring firms at 7:30 p.m. on Oct. 12 and began analyzing the security breach incident. It reported the possibility of a customer information leak to the Financial Supervisory Service at 8:40 a.m. on Oct. 13 and confirmed the leak at 8 a.m. on Oct. 15.

OK Savings Bank said it reported the personal data leak to relevant authorities at 9 a.m. on Oct. 15 and began individually notifying affected customers from 9:10 a.m.

It is informing customers of the leak by text message and email and urging measures to prevent secondary damage, including not clicking links from unknown sources and using a safe-blocking service. It also plans to operate a dedicated counseling window for damage reports and consultations.

OK Savings Bank said it completed measures including blocking suspected hacking IP addresses and access routes and strengthening emergency security checks and monitoring of systems. It said no additional unusual signs have been confirmed so far.

An OK Savings Bank official said, "We deeply apologise for causing concern to our customers," and added, "We will re-examine the overall personal information protection framework and security system and do our utmost to strengthen security to prevent a recurrence."