**Disclaimer: The employee at T-World wished to stay anonymous due to potential employer backlash.
“Thank you, your information is encrypted and safe with us.” If you never questioned the candor of this message, it’s time for you to start. South Korea’s largest carrier, SK Telecom (SKT), faced a massive cyberattack that led to the theft of approximately 23 million customers’ personal data on April 19, 2025. This equates to about half of Korea’s 52 million residents.
The attack leaked sensitive Universal Subscriber Identity Module (USIM) data to an unknown source by infiltrating SKT’s Home Subscriber Server (HSS). The jeopardized information included customer’s phone numbers, used for SIM-cloning, which intercepts vital services that require two-factor identification. This enables common teen security concerns like Instagram hacks and online impersonation.
Although SKT successfully removed the malware from its servers a month after the attack, the leaked data remains untraceable. To repent, the company offered free USIM replacement service and other subscription benefits for the existing users.
Alas, this failed to satisfy the furious users. Ji-hoon Kim, a long-time subscriber of SKT, said, “When I read that my phone number and USIM information were stolen, I felt exposed. Even if SKT offered free USIM replacement, my data was already out in public.”
Over three months after the leak on July 28, the company introduced a “personal information check” system for users to identify their leaked information. It revealed that phone numbers, subscribers’ SIM identification numbers, USIM IDs, and 21 other types of internal personal information leaked from SKT’s database.
While the media forecasted a rise in scamming or impersonation calls using the leaked numbers, secondary harm has yet to occur. While the service did not report further suspicious aftermath, approximately 83,000 users transferred to other carrier services like KT or LG U+.
For many, the event breached trust. “I’ve been with SKT for over ten years, and I never imagined my personal data could be leaked like this, like a movie,” Kim said. “I decided to move to my new carrier, KT, as they have been more transparent about personal information security.”
Now, SKT attempts to restore their reputation. An anonymous employee from T-World, an SKT flagship store, addressed the loss of trust between the company and its customers. “We understand the criticism that our response was slow. That’s why we are currently increasing the user benefits and perks as an apology to the customers,” the employee said.
Unfortunately, the conglomerate’s untimely band-aid efforts preclude any recovery. Ms. Loustch, an SKT user since 2019, said, “They are trying to make up, but once it is out there, it’s out there.”
Until SKT closes the case by unveiling the criminals behind the attack, the public will grow increasingly hostile toward the carrier. Only time will tell if Korea’s largest carrier will restore its glory once more.
