With nearly half of South Korea’s mobile market share and around 34 million subscribers, SK Telecom holds a crucial position in the country’s telecommunications sector. In an official statement, the company explained that malware had infiltrated parts of its network, prompting immediate action to contain the threat.
The affected systems were isolated swiftly, and the malicious software was removed. So far, SK Telecom has stated there is no confirmed misuse of customer data linked to this breach.
This was reported to the Korea Internet & Security Agency (KISA) on April 20, and to the Personal Information Protection Commission.
Investigations are ongoing to determine how the attackers gained access and the extent of the data exposed.
USIM cards store essential data such as International Mobile Subscriber Identity (IMSI) numbers, phone numbers (MSISDN), encryption keys for network authentication, and sometimes even stored contacts or text messages. Unauthorized access to this information could enable cybercriminals to conduct targeted surveillance, track users’ locations, or perform SIM-swapping attacks that could compromise online accounts and digital assets.
In response, SK Telecom has strengthened security around USIM card management, increasing checks on SIM card replacement activities and monitoring authentication processes for suspicious behavior. Accounts showing irregular activities could face automatic suspension to prevent potential fraud.
Additionally, the carrier is advising customers to activate their USIM protection service, a preventive measure that restricts unauthorized SIM swaps, adding extra protection to user accounts.
A hacking group is yet to claim responsibility for the breach. SK Telecom emphasized that while the malware was neutralized quickly, they remain vigilant and are working closely with cybersecurity authorities to uncover more details about the intrusion and enhance future protections.
This breach highlights ongoing risks faced by large mobile operators, especially during periods when cyber defenses might be less robust. It also underscores the critical need for mobile carriers to adopt continuous security monitoring and proactive measures to protect customer data from emerging threats.
As investigations continue, SK Telecom has committed to updating customers and regulators about any new findings or developments related to the incident.
