Recently, SK Telecom (SKT) users in Korea were shocked to hear that their USIM (Universal Subscriber Identity Module) data had been leaked due to malware. While SKT officially announced the incident on April 22, they have not disclosed exactly what kind of information was leaked or who it was leaked to. Naturally, customers are anxious, wondering, "Is my SIM card safe?" and "Should I replace it immediately?"
In this guide, we will clearly explain everything foreigners living in Korea need to know about the SKT USIM data breach, free SIM replacement service, and USIM Protection Service.
Let's make sure you stay safe and informed!
Overview of the SKT USIM Data Breach
Background of the Incident
In April 2025, SK Telecom detected that customer USIM data had been compromised by malware. However, they have yet to reveal the specific details, such as whose data was leaked or how it might be used.
What Kind of Information Was Leaked?
Experts warn that the leaked data could potentially allow hackers to create cloned SIM cards. If successful, hackers could make calls, access financial services, or verify identities under your phone number.
Although SKT has stated that there have been no reported misuse cases yet, the risk still exists, and immediate action is recommended.
SKT’s Response and Customer Protection Measures
Free SIM Card Replacement Service
To reassure customers, SKT is offering a free SIM card replacement service. This service is available to all SKT customers, including foreigners residing in Korea.
Who can replace their SIM for free?
-
All SKT customers (Korean citizens and foreigners alike)
How to replace your SIM card:
-
Reserve online through the SKT T World website
-
Receive a text notification when your SIM is ready
-
Visit a designated SKT branch with your ID and current SIM card
What is the USIM Protection Service?
The USIM Protection Service prevents your SIM card from working on devices other than your own smartphone. Even if hackers clone your SIM, they won't be able to use it.
Pros and Cons of USIM Protection Service:
-
Pros: Protects against fraudulent use of your SIM
-
Cons: Disables overseas roaming and prevents switching to another phone
Important: If you plan to travel internationally, this protection service might not be ideal.
Important Tips for Customers
How Dangerous Is SIM Cloning?
Even if a hacker duplicates your SIM, the SKT network can detect multiple connections with the same number and automatically block both SIMs. This minimizes the risk.
However, if your phone is turned off, SKT cannot detect the cloning attempt immediately, which could temporarily allow unauthorized access.
Keep your phone turned on at all times for maximum protection.
How to Protect Your Personal Data
-
Keep your smartphone powered on
-
Avoid clicking suspicious links or messages
-
Enable two-factor authentication (2FA) for banking apps and online services
-
Regularly update your passwords
What You Need for SIM Replacement
-
Valid ID (passport or alien registration card)
-
Your current SKT SIM card
-
Online reservation confirmation (if applicable)
After replacing your SIM, double-check if your:
-
Calls and texts are working
-
Banking apps and mobile payments are functioning
-
Contacts and transportation cards are properly restored (especially for Android users)
Expert Opinions and Additional Recommendations
Advice from Cybersecurity Experts
Cybersecurity Professor Kim Yong-dae (KAIST) advises that the best way to stay protected is to keep your smartphone turned on. If your phone is off, hackers might exploit the gap and connect their cloned SIM.
Additional security tips include:
-
Set up OTP (One-Time Password) authentication for banks
-
Strengthen your phone lock with biometric options
-
Reconfigure SMS authentication after SIM replacement
Should I Consider an eSIM?
If you often travel overseas and need international roaming, using a separate data-only eSIM might be a smart alternative. Many eSIM plans are affordable and easy to activate nowadays.
Final Summary
According to SKT, there have been no confirmed cases of misuse yet. However, it's always better to act early and stay secure.
Here’s what you should do:
-
Reserve and replace your SIM card for free at SKT branches
-
Activate the USIM Protection Service to enhance security
-
Strengthen your online account security settings
Your smartphone is an important part of your identity and finances — protecting it is worth a little extra effort.
Visit the SKT website now to reserve your SIM card replacement and keep yourself safe!