The bank said Tuesday that the additional cases involving 460 employees and 1,631 customers were identified the previous day through an investigation conducted in cooperation with financial regulators and relevant agencies.
The bank earlier said it detected the data leak on Sept. 30 following an external attack on its mobile work system for employees that lasted about 43 hours. It disclosed the incident on Oct. 2, initially reporting that 119 people had been affected.
It apologized for failing to fully assess the scope of the incident in its initial investigation, adding that it would individually notify newly identified affected customers and inform them of measures to prevent further harm.
The country's largest bank also pledged to extend protective measures to affected customers and strengthen security measures to prevent similar incidents from recurring.
Its massive data leak was among a string of recent cyberattacks targeting financial institutions in South Korea, raising concerns about the protection of personal information and the security of digital banking systems.
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