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The Ministry of Science and ICT (MSIT) formally announced the conclusive findings of its investigation into the security incident at KT Corp. on Monday, December 29, 2025. The extensive probe determined that the core vulnerability stemmed from the mobile carrier's insufficient oversight and management protocols concerning its femtocell infrastructure, which are small base stations deployed for localized network enhancement. This systemic negligence created an exploitable environment, permitting the introduction of illicit femtocells that subsequently gained unauthorized ingress into KT's proprietary internal network architecture.

The security lapse resulted in two primary consequences: the facilitation of unauthorized mobile payment transactions and the extensive exposure of sensitive customer data. The financial fallout included unauthorized micropayments totaling 243 million won, approximately $167,000 USD, impacting 368 confirmed users. The scope of the data compromise was significantly broader, affecting 22,227 users whose personal identifiers, including mobile numbers, International Mobile Subscriber Identity (IMSI) numbers, and International Mobile Equipment Identity (IMEI) numbers, were exfiltrated.

Forensic analysis conducted by the joint government-private investigation team revealed a critical flaw in the device authentication mechanism. Specifically, all KT-issued femtocells shared an identical digital certificate issued by the manufacturer, a certificate possessing an extended expiration period of up to ten years. This configuration meant that once an attacker successfully copied this single certificate, unauthorized network access could be maintained for nearly a decade. Furthermore, the investigation uncovered a significant internal malware presence, identifying 94 KT servers infected with 103 distinct types of malicious code, including BPFDoor and Rootkit, with some infections dating back to April 2022.

The MSIT ultimately concluded that KT had demonstrably failed to uphold its contractual commitment to deliver secure services, placing all subscribers in a state of potential threat exposure. This incident follows a pattern of sector scrutiny, as KT's peer, SK Telecom, was previously fined 134.8 billion won for its own data breach. The Ministry has mandated that KT immediately institute stringent security enhancements, including the regular rotation of the authentication server's IP address and the establishment of robust detection systems for unauthorized femtocell connections. KT is obligated to furnish a comprehensive remediation plan within one month, with a follow-up government inspection scheduled for June 2026 to verify compliance.

Due to the severity of the security failures, the MSIT signaled that mobile carriers across the board might soon face directives to waive cancellation fees for users migrating to competitors. Separately, law enforcement authorities reportedly apprehended two Chinese nationals in connection with the financial fraud aspect of the case. In a parallel development, the MSIT reported an obstructive outcome in its separate investigation concerning a data breach at LG Uplus Corp., initially disclosed in July 2025. The ministry asserted that LG Uplus engaged in improper conduct by submitting falsified documentation and reinstalling operating systems on affected servers after receiving guidance from the Korea Internet & Security Agency (KISA), actions that severely impeded a thorough forensic investigation. While the leak of information from LG Uplus's integrated password management solution, APPM, was confirmed, the obstruction led the MSIT to formally request a police investigation into LG Uplus on suspicion of obstructing official duties.

Key servers along the network path were reinstalled or discarded between August 12 and September 15, following KISA's intrusion guidance on July 19. Science Minister Bae Kyung-hoon underscored the gravity of the situation, emphasizing that information security is a fundamental prerequisite for corporate viability and the maintenance of a trustworthy service ecosystem for the nation. The ongoing regulatory actions signal an elevated commitment from the South Korean government to enforce accountability in critical infrastructure security.