Woori Bank has reported a data breach involving the personal information of approximately 17,000 customers.

In a notice to customers today (July 3), Woori Bank stated, "A data leak occurred due to the negligence of an employee at an external development firm, which had been holding 17,551 pieces of personal information without authorization."

The leaked information consists of Connecting Information (CI), which is encrypted data used for online personal identification, and customer nicknames.

According to the bank, this information was shared with the external developer during a project to build a non-fungible token (NFT) platform in September 2024.

Although the project has since concluded, an employee at the firm kept the data without authorization and subsequently shared it on a developer platform, leading to the leak.

"Upon becoming aware of the leak on June 30, we immediately blocked access to the information through the development firm, reported the incident to the Personal Information Protection Commission, and posted a notice on our website," the bank stated.

The bank added, "As of now, we have found no evidence that the leaked information has been spread or misused online or offline."

Regarding the nature of the leaked data, the bank emphasized, "Customer nicknames are arbitrary aliases and are not member IDs or login credentials. Furthermore, Connecting Information is a value used to identify individuals online and cannot be used to identify a specific person unless combined with other data."

Nevertheless, to prevent potential damages such as voice phishing or smishing, Woori Bank urged affected customers to exercise extreme caution regarding calls from unknown numbers and to avoid clicking URL links in text messages.

The bank also added that it is applying a separate Fraud Detection System (FDS) to prepare for any unforeseen incidents.

"We will use this incident as an opportunity to conduct a full inspection of personal information management practices at our development partners and rectify any shortcomings," Woori Bank said. "Should any damage occur to our customers, we will identify it and provide compensation as quickly as possible."