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| SK Telecom got hacked |
In one of the most serious cyberattacks ever recorded in South Korea, SK Telecom has confirmed a data breach affecting SIM card information of some of its 23 million mobile subscribers.
The incident prompted an emergency response from the Ministry of Science and ICT and the Korea Internet & Security Agency (KISA), who launched an on-site investigation at SK Telecom’s headquarters on April 22.
According to SK Telecom, the breach primarily involved USIM card data, which includes:
- Mobile phone numbers
- Device identification numbers (IMEI)
The company has assured the public that sensitive personal data such as resident registration numbers, birth dates, and payment information were not compromised. However, the Ministry of Science is conducting further checks to confirm that no additional personal data was leaked.
Since SK Telecom’s subscriber data is stored across multiple systems, the verification process is expected to take time.
The compromised system was an authentication server used by both LTE and 5G networks. This server validates user identity during calls by matching the SIM and device data.
It remains unclear how hackers gained access to the server or if any malware was installed. So far, no misuse of leaked SIM data has been reported.
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| SK telecom head apologizes over the hacking incident |
The telecom giant is now offering:
- Free USIM card replacements for all affected customers, including those on affiliated MVNO (virtual mobile network) plans
- Refunds for customers who have already replaced their SIM cards on their own
- Enhanced security measures to protect user accounts from secondary harm
Starting April 28, customers can visit SK Telecom stores nationwide, including locations at airports, to receive their free SIM card replacement.
If the investigation reveals any negligence in security management, the South Korean government may demand corrective actions from SK Telecom. Authorities have also stated that they are prepared to form a joint public-private task force to thoroughly investigate the cause and propose preventive solutions.
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| SK Telecom notifications regarding the hacking incident. |
ℹ️ What is USIM?
A USIM (Universal Subscriber Identity Module) is a small chip inserted into mobile phones to store:
- The subscriber’s phone number
- The device identification code
It’s used to authenticate the user on mobile networks. Importantly, personal contact data stored on the SIM card itself was not uploaded to the compromised server and is therefore safe.
⚠️ What Should Users Do?
South Korean authorities urge SK Telecom users to:
- Remain vigilant against potential misuse of leaked data
- Check your mobile account for unusual activity
- Replace your SIM card if you’re concerned
📌 Summary of SK Telecom Data Breach Incident
- Date of Discovery: April 22, 2025
- Company Affected: SK Telecom
- Data Leaked: Mobile number, IMEI (SIM card info only)
- Sensitive Data: Not exposed (based on current investigation)
- Customers Affected: Part of SKT's 23 million subscribers
- Free SIM Replacement: Begins April 28 at SKT stores & airports
- Government Action: On-site investigation; possible joint task force
- Public Response: Company apologized; no misuse cases reported so far