SK Telecom reveals malware intrusion that remained hidden for nearly two years, led to the leaking of 26.69 million IMSI units and 9.82 GB of USIM data. Discover the telco’s security upgrades & future plans after the massive breach.
A recent data breach at South Korean telecommunications giant SK Telecom was, reportedly, much more deeply rooted than initially thought, with the intrusion remaining hidden for nearly two years. The company announced on Monday that the malware has gone undetected since at least June 2022.
The attack, disclosed in April, affected a significant portion of SK Telecom’s 23 million customers, compromising personal and financial details. The Ministry of Science and ICT, along with a joint team of public and private investigators, revealed that the attack compromised a significant portion of SK Telecom’s user data.
Specifically, approximately 26.69 million International Mobile Subscriber Identity (IMSI) units were leaked. IMSI is a unique 15-digit or shorter number that identifies and authenticates each mobile subscriber. Moreover, investigators identified 25 types of malware and quarantined 23 affected servers, claiming that 9.82 gigabytes of USIM information were compromised.
Responding to the Breach
In response to the security lapse, SK Telecom has implemented a series of preventative measures. The company has temporarily stopped new subscriber sign-ups and initiated a nationwide program to replace SIM cards as a safeguard.
Furthermore, they have rolled out an upgraded fraud detection system, FDS 2.0, which uses a “triple-factor authentication” process to prevent unauthorized SIM and device cloning. This enhanced security is now automatically applied across their network.
SK Telecom has also emphasized that no actual customer damages or instances of “terminal cloning” have been reported so far and all attempts at phone or SIM card piracy are now blocked at the network level, with three layers of verification to confirm the legitimacy of the subscriber, SIM card, and device. The company has pledged to “take full responsibility for any damages” that may arise from the breach, offering to replace the USIM of all 25 million subscribers, including 2 million budget phone users, for free.
National Security Concerns and Future Steps
SK Group chairman Chey Tae-won issued an apology to customers earlier in May, highlighting the severity of the incident by stating it “needs to be looked at as a matter of national defence.”
The malware used in the attack is believed to be BPFdoor, which can bypass authentication. It is typically used by hacking groups linked to China. Although no specific group has claimed responsibility, the chairman’s concerns and the identified malware align with similar tactics observed in recent attacks on US telecom companies.
Beyond technical upgrades, SK Telecom is also enhancing customer support. Starting May 19, the company plans to offer “mobile service” visits to remote areas, explaining SIM protection services and providing on-site SIM replacements and resets. These efforts highlight the company’s commitment to rebuilding customer trust and strengthening cybersecurity to counter cybersecurity threats.