South Korea’s privacy watchdog has fined wireless carrier KT Corp. 53.9 billion won ($37.4 million) after a major data breach exposed the personal information of 16,647 users through unauthorised mobile base stations.
The regulator has also ordered the company to strengthen its security measures.
According to the Personal Information Protection Commission, the breach affected users’ phone numbers and mobile device identification numbers. The stolen information was later used to carry out unauthorised transactions, resulting in total losses of 240 million won for 368 victims.
The regulator said hackers gained access to KT’s wireless network between Oct. 8, 2024, and Sept. 5, 2025. The breach reportedly went undetected during this period, and the company became aware of the incident only after receiving a complaint from a user.
Following the investigation, the watchdog instructed KT to improve the security of its wireless network equipment and strengthen its personal information protection practices.
KT CEO Kim Young-shub admitted during a parliamentary hearing that the company had poorly managed femtocells, which are small, low-power cellular base stations commonly used in homes and small businesses.
“After the incident, we reviewed the management of femtocells and found numerous vulnerabilities and poor management,” Kim said. “We have since taken measures to prevent illegal femtocells from connecting to the network.”
Kim also said KT outsources the installation and management of femtocells. According to the company, unregistered femtocells connected to its network around late August, allowing access to the private data of 362 users and causing estimated losses of 240 million won ($173,000).
He further stated that KT is expanding its investigation to cover all authentication data after lawmakers pointed out that the company’s earlier probe focused only on breaches involving the automated response system (ARS).
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