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Cyberterrorism

SK Telecom Cyberattack Exposes 26.9 Million Customers' USIM Data

Strategic Insights

— 1 min read

A devastating cyberattack on South Korean telecom giant SK Telecom has compromised the personal information and USIM data of all 25 million subscribers. The breach, which occurred in June 2022, was only recently discovered by the company on April 18, 2025. Investigators believe that 9.32 gigabytes of USIM data, containing 26.9 million international mobile subscriber identity (IMSI) numbers, have been leaked. The IMSI and IMEI numbers are unique identifiers for each user and device, respectively, on a network and could potentially be exploited in financial transactions.

Key Takeaways:

  • The cyberattack compromised 23 SK Telecom servers, with 15 of them analyzed by the joint government-private investigation team, revealing 25 malware variants.
  • Investigators found 9.32 gigabytes of USIM data, equivalent to 26.9 million IMSI numbers, have been leaked, posing a significant risk of identity theft and financial fraud.
  • SK Telecom has 25 million subscribers, including 2 million budget phone users, and has offered to replace the USIM of all users free of charge to prevent user damage.
  • The company has also enrolled all users in its USIM protection service, which offers the same level of protection against unauthorized financial activities as a physical USIM replacement.
  • The Ministry of Science and ICT has confirmed that it is unlikely that hackers can duplicate a smartphone using only the leaked IMEI numbers.
  • The Personal Information Protection Commission will determine whether SK Telecom violated the Personal Information Protection Act by keeping log records only for four months and by failing to encrypt the leaked personal information.

Statistics:

  • 25 million subscribers affected by the cyberattack
  • 26.9 million IMSI numbers leaked
  • 9.32 gigabytes of USIM data compromised
  • 15 servers analyzed by the investigating team
  • 25 malware variants found on analyzed servers
  • IMEI numbers are 15-digit unique identifiers for each device
  • 2 million budget phone users among the affected subscribers

Sources:

  • Yonhap News Agency
  • Joint government-private investigation team report (no specific date mentioned)
  • Personal Information Protection Commission
  • Ministry of Science and ICT

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