USIM data is information stored on a Universal Subscriber Identity Module (USIM), which typically includes International Mobile Subscriber Identity (IMSI), Mobile Station ISDN Number (MSISDN), authentication keys, network usage data, and SMS or contacts if stored on the SIM. South Korea's largest mobile operator, SK Telecom, is warning that a malware infection allowed threat actors to access sensitive USIM-related information for customers. While SK Telecom says there is no evidence that the leaked data has been abused, the company has strengthened blocks of USIM swaps and abnormal authentication attempts and will immediately suspend service for accounts linked to suspicious activity. SK Telecom is the largest mobile network operator in South Korea, holding approximately 48.4% of the mobile phone service market in the country, corresponding to 34 million subscribers. Bill Toulas Bill Toulas is a tech writer and infosec news reporter with over a decade of experience working on various online publications, covering open-source, Linux, malware, data breach incidents, and hacks. Subscribers are recommended to sign up for USIM protection service through this portal, which blocks mobile numbers from being ported to another SIM card when enabled. The breach was reported to the Korea Internet & Security Agency (KISA) the following day, and the country's Personal Information Protection Commission was notified earlier today.
This Cyber News was published on www.bleepingcomputer.com. Publication date: Tue, 22 Apr 2025 18:30:08 +0000