On October 27 an outsider broke into Bithumb's in-house mobile groupware, Daou Technology's Daou Office, which staff use for work and messaging. Customer files shared by employees inside the app ended up in the leaked data at the Korean exchange.

Of 6,444 affected customers, 844 had personal data exposed, including resident registration numbers, driver's license numbers, bank account numbers and ID copies. Files of the other 5,600 were encrypted. Data of 715 employees also leaked.

Bithumb says the groupware runs separately from trading services and customer assets, and no funds have been reported lost. The exchange first notified regulators, KISA and the Personal Information Protection Commission about the employee leak only, and found the customer data later during its own probe.

The breach adds to a run of incidents in Korean crypto this month: GOPAX operator Streami flagged abnormal access to some accounts, and Prabang lost 1 billion won to a hack. CEO Lee Jae-won apologized and promised compensation if secondary damage is confirmed.