Information on customers of two major foreign banks in South Korea has been leaked, sources said Wednesday, spawning concerns about an online security breach.

Personal data of some 130,000 customers of Standard Chartered Bank Korea and Citibank Korea leaked from branches in the southern city of Changwon, South Gyeongsang Province, according to the sources.

Bank officials related to the incident were taken into custody to be interrogated, they said.

Representatives at the banks said they are in the process of confirming the details.

If confirmed, the extent of data leaks would be the largest in the history of the banking sector in South Korea.

The incident follows reports that the two foreign banks are suffering from weak earnings amid the slowing economy and squeezed margins.

SC Bank is in the process of cutting its branches by as many as 100 in Korea to 250. The Korean unit of U.S.-based Citibank has also closed nearly 10 percent of its branches through November due to falling profits.

The need to beef up local banks’ computer security has been consistently raised due to a series of computer data leaks and hackers’ attacks on online financial transactions since 2011.

In late March, network systems at local banks, including Nonghyup Bank and Shinhan Bank, were hacked into by an unknown malware, although no personal information was leaked. (Yonhap News)