Mirae Asset Securities, South Korea's largest brokerage by market capitalisation, says hackers leaked the personal information of about 39,000 customers and employees in attacks on Wednesday and Thursday this week. The company disclosed the breach on Saturday 7 November.

Account numbers belonging to about 3,800 customers were leaked, the company said. Account holders' names and other customer details did not leak with them. The personal data of 35,255 current and former employees and contractors was also exposed, including names, employee numbers, email addresses, mobile phone numbers and encrypted passwords. Resident registration numbers, passport numbers and driver's licence numbers were not exposed.

The attackers hit a mobile-web login service using phone authentication on Wednesday 4 November, and the brokerage's in-house groupware system, mi-global, on Thursday 5 November. Mirae Asset said it blocked the affected routes after detecting suspicious activity from external IP addresses and activated its emergency response system. It reported the incident to the Financial Services Commission, the Financial Supervisory Service and the Personal Information Protection Commission. No malware or service disruption was involved, and no financial damage has been confirmed so far.

Fourth Mirae affiliate hit in under two weeks

Mirae Asset Securities is the fourth Mirae Asset Group affiliate hit by a cyber intrusion since 26 October, after Mirae Asset Life Insurance disclosed a customer data leak that day, with intrusions later detected at Mirae Asset Global Investments and another group asset manager. Daishin Securities said on 28 October that the personal data of 38,490 customers had leaked.

South Korea's financial regulator says more than 470,000 personal data records have leaked from 37 financial firms over the past month, with about 1 billion won ($745,000) stolen. Mirae Asset urged customers to beware of calls, texts and emails impersonating the company, and opened a temporary help desk on Saturday.