Authorities in South Korea have launched an investigation into a reported data breach that lead to the theft of funds from Bithumb, the country’s largest bitcoin and ethereum exchange by trading volume.

According to Yonhap News, Bithumb contacted state-run internet watchdog Korea Internet and Security Agency last week to report that “its data on customers was leaked” after “one of its employees’ home personal computers was hacked.”

The exchange confirmed the hack in a notice, which stated that “the accident was caused by an external infringement accident,” noting that the breach “is independent of Bithumb’s internal network, server and virtual wallet, and all members’ original (fiat) and virtual currency deposits are safe.”

The exchange estimated that personal data on about 30,000 of its customers, or 3 percent of its members, have been compromised. MK News reported that the stolen data did not contain any of the customers’ passwords, but it includes personal information such as email addressed and telephone numbers, which authorities said could be used in voice phishing scams.