SUMMARY:

SK Telecom, a major telecommunications company in South Korea, experienced a cyberattack and subsequent data breach on April 18, 2025. The cyberattack compromised sensitive Universal Subscriber Identity Module (USIM) data, potentially impacting millions of customers. The hackers infiltrated SK Telecom’s Home Subscriber Server (HSS), enabling unauthorized access to USIM data, including authentication keys. Leaked USIM data could enable SIM-cloning, where attackers hijack phone numbers to intercept multifactor authentication codes, access banking apps, or perpetrate identity theft. SK Telecom is actively addressing the breach by enhancing security measures and offering free USIM replacements to affected customers. Immediate action is critical to mitigate risks, and customers are urged to replace their SIMs and enroll in protective services to safeguard their personal information.

The South Korea Ministry of Science and ICT said that phishing attack attempts using the keywords 'free SIM replacement' and 'USIM protection service' are occurring, and asked users to be careful.

RECOMMENDATIONS:

For SK Telecom customers, the following actions are recommended:

• Replace USIM: Visit T World stores or airport kiosks starting April 28, 2025, to replace your SIM or eSIM. Make reservations via SK Telecom’s portal or app to avoid delays.

• Enroll in USIM Protection Service: Available on SK Telecom’s website or T World platform to prevent unauthorized SIM changes. ** Reference the JoongAng link if planning to use overseas roaming

• Post-Replacement Actions: Reauthenticate banking apps, reinstall the PASS identification app, and monitor accounts for suspicious activity.

• Global Measures: The USIM Protection Service will be enhanced for overseas roaming starting May 2025.

For further details or to access SK Telecom’s USIM replacement program, visit www.sktelecom.com or contact their customer service portal.

REFERENCES:

The Korea Herald - SK Telecom systems breached in cyberattack
https://www.koreaherald.com/article/10471148

Yonhap - SK Telecom begins hacking-prompted USIM replacement service
https://en.yna.co.kr/view/AEN20250428007400320

**JoongAng Daily - SKT hack: Do I need a new SIM? How do I replace it? Your questions answered.
https://koreajoongangdaily.joins.com/news/2025-04-29/business/industry/SKT-hack-Do-I-need-a-new-SIM-How-do-I-replace-it-Your-questions-answered/2295531

NATE - 'Free SIM replacement' phishing scam on the rise (Korean)
https://news.nate.com/view/20250427n15649