South Korea's second-largest mobile operator KT Corp announced on Thursday that personal data of over 5,500 users may have been compromised in a recent mobile payment data breach, for which the company has issued a public apology.

In a statement, KT Corp said: "We have confirmed that International Mobile Subscriber Identity (IMSI) data may have been leaked, affecting 5,561 users. We reported this incident to the Personal Information Protection Committee (PIPC) this afternoon and have notified affected customers via text message regarding remedial measures."

KT Corp CEO Kim Young-shub also apologized at a press conference and pledged full compensation.

"We sincerely apologize to all customers affected by the unauthorized mobile payments. We will make every effort to prevent further damage and provide full compensation to the victims," he stated.

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

The South Korean government has established a joint task force to investigate the incident.

In April this year, SK Telecom disclosed a serious Universal Subscriber Identity Module (USIM) data breach on its servers, affecting more than 23 million users. The Personal Information Protection Committee (PIPC) imposed a record fine of 134.8 billion won (approximately $96.9 million) on SK Telecom last month, marking the highest penalty since the agency's establishment in 2020.