SK Telecom Malware Attack Exposes USIM Data in South Korea

SK Telecom, South Korea’s top mobile carrier, has disclosed a security incident involving a malware infection that exposed sensitive information tied to users’ Universal Subscriber Identity Modules (USIMs). The breach was detected on the night of April 19, 2025, during the weekend when many companies operate with reduced cybersecurity staffing. 

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 a

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