Key Points

"We confirmed a possible leak of international mobile subscriber identity (IMSI) data affecting 5,561 users," KT said in a statement. "We reported the case to the Personal Information Protection Commission (PIPC) this afternoon and notified affected customers via text message about relief measures."

Kim Young-shub, chief executive officer (CEO) of KT, also apologised at a press conference, pledging full compensation, reports Yonhap news agency.

"We sincerely apologise to all customers affected by unauthorized mobile payments," he said. "We will do our utmost to prevent further damage and provide full compensation to victims."

Since August 27, some KT users, mostly in southwestern Seoul, have reported unauthorized mobile transactions.

The government has launched a joint special team to probe the incident.

KT said the IMSI data may have been exposed after illegal, unregistered micro base stations connected to its communication network. IMSI data, a unique identifier for each subscriber stored in a universal subscriber identity module (USIM) chip, can be misused if leaked.

It said about 19,000 customers' mobile phones had connected to the illegal base stations at least once, though not all of them experienced unauthorized financial transactions.

Of those, the IMSI data of 5,561 customers was possibly leaked, the company added.

As of Wednesday, authorities have confirmed 278 cases of unauthorized mobile payments worth 170 million won ($122,000) reported by KT users.

KT said it will support all 19,000 affected customers by replacing USIM chips free of charge and providing a USIM protection service.

The recent breach at KT came just months after SK Telecom Co. reported a massive data leak that affected more than 20 million users, raising public concerns over data protection at local telecom companies.

- IANS