Woori Bank headquarters in central Seoul (Newsis) The personal information of 17,551 Woori Bank customers was leaked after an employee at an external software developer retained customer data without authorization and uploaded it, the bank said Friday.The leaked information included connecting information, or CI, an encrypted identifier used to verify individuals online, as well as customer nicknames. Phone numbers, resident registration numbers and home addresses were not compromised, according to the bank.The affected customers had expressed interest in using Woori Bank's nonfungible token platform and consented to the sharing of their personal information for the service.Woori Bank said it provided the data to the external developer in September 2024 during the development of the NFT platform. After the project was completed, an employee at the developer retained the information without authorization and later uploaded it to a developer platform, resulting in the leak.The bank said it became aware of the incident on Tuesday and immediately worked with the developer to block access to the exposed data. It also reported the case to the Personal Information Protection Commission and notified affected customers through its website.Woori Bank said it has found no evidence that the information has been further distributed or misused. However, it warned that the leaked CI could be exploited if combined with personal information exposed in other data breaches.The bank urged affected customers to remain cautious of suspicious phone calls, text messages and links from unknown sources.