On April 19, 2025, a major SK Telecom USIM data breach compromised the information of approximately 23 million customers. This comprehensive guide covers everything from registering for USIM Protection Service and free USIM replacement to enhancing account security. Learn about essential re-authentication procedures after USIM replacement and long-term security enhancement methods.
Table of Contents
USIM Hacking Incident Overview and Response
On April 19, 2025, SK Telecom's internal servers were infected with malware, resulting in a data breach that exposed USIM information of approximately 23 million subscribers. This incident goes beyond a simple data leak, raising serious concerns about potential secondary crimes such as phone cloning, financial account theft, and cryptocurrency wallet hacking.
1 Incident Details
SK Telecom USIM Information Leak
SK Telecom took immediate action following the malware infection, reported the incident to government agencies, and implemented measures to protect affected customers.
- Incident Cause: Malware infection in internal servers leading to USIM data breach
- Scope of Impact: Approximately 23 million subscribers' USIM-related information
- Reporting Status: Reported to KISA on April 20 and to the Personal Information Protection Commission on April 22
- Current Status: Malware removed, affected equipment isolated
💡 SK Telecom has stated that no concrete cases of information misuse have been reported so far, but the company and government agencies continue to monitor the situation closely.
2 SK Telecom's Response Measures
SK Telecom's CEO has personally issued a public apology and pledged to cooperate with the joint government-private investigation team to transparently disclose information as the cause and scope of the incident are fully identified. The company has confirmed that MVNO (Mobile Virtual Network Operator) users are also eligible for free USIM replacement and plans to secure an additional 5 million USIMs by the end of May to address potential supply shortages.
USIM Protection Service and Replacement Guide
The first essential steps to prevent damage from the SK Telecom USIM hacking incident are registering for the 'USIM Protection Service' and getting a 'free USIM replacement.' The USIM Protection Service is particularly important as it's free, immediately effective, and offers the same level of protection as physically replacing your USIM.
1 How to Register for USIM Protection Service
USIM Protection Service Registration Process
This service prevents unauthorized use of your USIM information or phone cloning, even if your data was compromised. Registered users receive 100% compensation for any hacking damage.
- T World App Registration:
- Open T World app → Log in
- Tap 'More' at the bottom → 'USIM/Device' → 'USIM Protection Service'
- Tap 'Apply' button → Confirm
- T World Website Registration:
- Visit T World website → Log in
- 'Subscribe/Change' → 'Add-on Services' → 'USIM Protection Service'
- Click 'Apply' button → Confirm
- Call Center Registration: Call 080-800-0577 (SK Telecom Customer Service)
How to Get Free USIM Replacement
SK Telecom is offering free USIM replacement at all 2,600+ T World stores and airport roaming centers nationwide to address customer concerns. MVNO users are also eligible for replacement.
- In-store Replacement:
- Visit any T World store (bring ID)
- Request free USIM replacement
- Receive and activate new USIM
- Online Reservation:
- Visit care.tworld.co.kr
- Verify identity and select a nearby store
- Choose reservation time → Complete reservation
- Visit store at scheduled time for replacement
- Cost Reimbursement: Customers who replaced USIMs at their own expense between April 19-27 will be reimbursed
USIM Replacement Precautions
Please note these important precautions when replacing your USIM:
- Bring proper identification (enhanced identity verification)
- Back up important data before replacement as rebooting may be required
- If roaming abroad, replace your USIM immediately upon return (replacement during roaming will disable communication)
- MVNO users should check with their respective carriers for guidance
- Contact SK Telecom Customer Service (080-800-0577) before visiting to avoid congestion
You can register for USIM Protection Service and replace your USIM simultaneously. The Protection Service is particularly valuable as you can register immediately, even before physically replacing your USIM. Using the reservation system can reduce wait times, and if store visits are challenging, registering for the Protection Service alone provides significant security benefits.
Essential Re-authentication After USIM Replacement
After replacing your USIM, you'll need to re-authenticate various services that use your phone number for verification. This thorough process ensures continued service access and enhanced security.
1 Financial and Authentication Service Reset
Many financial apps automatically log you out after a USIM change. Complete the re-authentication process from the login page, and remember to reset two-factor authentication (2FA) for services that use it. Mobile banking may require re-registration in some cases, so follow the specific instructions provided by each banking app.
2 Google/Apple Accounts and SNS Re-authentication
Google and Apple Account Phone Number Updates
After replacing your USIM, you'll need to update your account information on global services like Google and Apple. These services use your phone number for authentication, two-factor authentication, and account recovery.
- Google Account Update:
- Visit myaccount.google.com
- Go to 'Personal Info' → Select 'Phone number' option
- Check your existing number and modify if needed → Verify with authentication code
- Also check and reset two-factor authentication (2FA) settings
- Apple Account Update:
- Visit account.apple.com or go to 'Settings > [Your Name] > Login & Security' on your iPhone/iPad
- Select 'Primary Phone Number'
- Remove existing number or replace with new one → Verify with authentication code
- Also update 2FA and recovery phone numbers ('Trusted Phone Number')
SNS and Messenger Phone Number Verification
Phone number-based SNS platforms like KakaoTalk and LINE require re-authentication after USIM replacement. Some apps may automatically prompt for re-verification.
- KakaoTalk:
- Open KakaoTalk app → 'Settings' → 'Account' → 'Change/Verify Phone Number'
- Confirm current number → Enter verification code → Complete
- Other SNS/Apps:
- Access 'Settings' or 'My Profile' menu in each app
- Go to 'Account Settings' → Find 'Phone Number' option and re-verify
- Also check security settings (2FA, etc.) if necessary
3 Long-term Security Enhancement Methods
💡 SMS-based authentication can be vulnerable to SIM cloning attacks. When possible, use app-based authentication like Google Authenticator, Microsoft Authenticator, or physical security keys (such as Yubikey) for better security.
After replacing your USIM, approach all authentication procedures as if setting them up for the first time. Prioritize re-authenticating financial apps and identity verification services. This is also an excellent opportunity to enhance your security by switching from SMS authentication to app-based authentication, which provides much stronger protection against similar attacks.
Tip
The top priorities for responding to the SK Telecom USIM hacking incident are registering for USIM Protection Service and getting a free USIM replacement. After taking these steps, it's essential to re-authenticate all phone number-based verification services. Pay special attention to financial apps, identity verification apps, Google/Apple accounts, and SNS platforms.
Use this incident as an opportunity to upgrade your security by switching from SMS-based authentication to app-based authentication and updating passwords for important accounts. If you notice any suspicious activity after replacing your USIM (unknown login attempts, unexpected authentication codes, etc.), report it immediately to both the carrier and relevant services.
💡 For additional inquiries, contact SK Telecom Customer Service (080-800-0577). Support is available 24/7.
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