South Korea's financial watchdog plans to launch an investigation next week into the leak of personal data from 420,000 customers of a major financial firm, Hyundai Capital, officials said Saturday.

The company, whose president returned to South Korea from an overseas trip earlier in the day, also began its own probe into the leak, which prompted the firm Friday to ask its 2 million customers to change their passwords to prevent further leaks.

The Seoul-based company, which specializes in personal loans, home mortgages and auto financing, said this week it was blackmailed by an unnamed hacker demanding money in return for not releasing the data.

The company, which stressed that key data required for financial transactions was not leaked, said names and home addresses of as many as 420,000 of its some 2 million customers were stolen. It remains unconfirmed whether their mobile phone numbers or e-mail addresses were disclosed as well.

The Financial Supervisory Service, South Korea's national financial watchdog, said its investigation will start in earnest on Monday.

"Investigators will be dispatched to look into the cause of the breach, the possibility of additional leaks and the contents of stolen information," an official said.

(Yonhap News)