A hacking incident involving digital asset exchange Bithumb's internal systems was confirmed to have leaked personal information of 6,444 customers. Of those, 844 had personal data directly exposed, including resident registration numbers and copies of identification.

Bithumb said in a website notice on Oct. 29 that an unauthorised external party infiltrated its internal mobile groupware system, Dawoffice, on Oct. 27, leaking personal information of customers and employees.

The leaked customer information covered a total of 6,444 people. Bithumb said information for 5,600 customers was leaked in encrypted file form, while the remaining 844 had details directly exposed, including names, mobile phone numbers, email addresses, resident registration numbers, driver's licence numbers, bank account numbers and copies of identification.

Personal information for 715 employees was also leaked.

The incident occurred between 11:28 a.m. and 12:27 p.m. on Oct. 27. Bithumb said it detected abnormal access at 12:14 p.m. that day and carried out emergency security measures, including blocking the attacker's access route and use of the system.

It reported the breach to the Korea Internet & Security Agency on the day of the incident and informed the Personal Information Protection Commission the next day about the leak of employee information.

At the time, it said, it had not confirmed whether customer information had been leaked. Bithumb later identified the customer data leak while further analysing the scope of damage and disclosed it additionally on Oct. 29.

The leaked information was believed to have come from materials saved or processed when Bithumb employees used the internal mobile groupware system in the course of their work.

Bithumb said the breached internal system is separated from systems that manage customers' exchange accounts and asset holdings, and it has not confirmed signs that exchange services or the customer database were directly compromised.

Bithumb said it will individually notify customers whose personal information was leaked from the afternoon of Oct. 29 about the damage and other details.

It also urged customers not to respond to contacts impersonating Bithumb employees that request authentication codes or induce app installations, and to use the official customer centre for damage reports or inquiries.

Bithumb Chief Executive Officer Jae-won Lee (이재원) said, "I deeply apologise for causing concern and anxiety to our customers." He added, "If secondary damage to customers whose personal information was leaked is confirmed, we will do our utmost to provide relief and compensation."

Lee added, "Using this incident as a turning point, we will re-examine the security system across our internal work infrastructure from the ground up and make every effort to prevent a recurrence."