SK Telecom offers new SIM cards to customers after revealing cyberattack

SK Telecom, South Korea’s largest mobile carrier and broadband provider, announced on Monday it will offer free SIM card replacements to customers after admitting a major data breach hit the telecommunications company earlier this month.

With over 23 million customers representing about 50% of the nation’s market share, SK Telecom (SKT) boasts its own music platform, operates several professional sports teams, recently launched Korea’s largest AI semiconductor manufacturing company, and has its own strategic investment division, SKT Americas, operating out of Silicon Valley, California.

It’s also the second breach in April for the telecom’s parent conglomerate, SK Group. On April 10th, the South Korean multi-manufacturing and services giant was claimed by the Qilin ransomware group, along with an alleged 1TB cache of stolen files.

Cybernews can confirm on Monday that the Telecom subsidiary was not listed on Qilin’s dark leak site. However, if a ransom demand were paid to the Russian-linked group, it would be customary to remove that company from the list of victims.

Furthermore, it appears SK Group has been taken off the Qilin leak site, but its unclear if the breaches are connected.

The company has not responded to Cybernews’ previous request for comment, nor has it revealed if any data was exfiltrated from its systems. Additionally, SK Telecom has not disclosed the type of data breached or how much.

CEO has “heavy heart”

SK Telecom CEO Yoo Young-sang held a public press conference on Sunday announcing the customer data breach, said to be “caused by malware,” as well as posting on social media.

“I stand here today with a heavy heart. We would like to sincerely apologize for the inconvenience and concern caused to customers who have trusted and used SK Telecom and to society due to the cyber breach that occurred on Friday, April 18,” the CEO said.

SK텔레콤은 고객 정보 보호를 위해 유심보호서비스(무료)를 제공하고,
FDS 이중 안전 시스템을 최고 단계로 격상해 운영 중입니다.

📢FDS(Fraud Detection System)란?
불법 유심으로 비정상 인증을 시도하는 행위를 실시간 탐지·차단합니다.

🔽유심보호서비스 가입하기🔽
https://t.co/xlJAofX2AG pic.twitter.com/P7PtRbkm0Y

undefined SK telecom (@SKtelecom) April 28, 2025

Announcing the free SIM swap service, the company, which boasted an annual revenue of over $10 billion in 2024, stressed its commitment to “analyze the cause of the incident and determine the extent of the damage in cooperation with relevant authorities.”

SKT additionally said it was checking the security status of all its servers and systems to prevent any further damage to customers.

This includes the managing of the telecoms “FDS (Fraud Detection System) system, which blocks authentication attempts of illegally copied SIM cards, at the highest level.”

Free SIM replacement for all

SK Telecom said it “will continue to implement ‘double and triple’ safety measures until the concerns and worries of customers due to this accident are resolved.”

As for the SIM replacement, which began on Monday, April 28th, customers, including those from other carriers that piggyback off the SKT network, can visit any of the approximately 2,600 T World stores or airport roaming centers to receive the card for free.

Alternatively, customers can also schedule an in-person appointment through the carrier's new online reservation system, which is specifically dedicated to handling SIM replacements. If a customer decides to replace the SIM card themselves, SKT will reimburse them, it said.

The CEO said updates will be provided to customers once more details about the attack is gleaned from the investigation.

SK Group is the second largest family-run conglomerate in South Korea, only behind Samsung.

The conglomerate operates more than 175 companies globally, including those in the Information and Communications Technology (ICT), advanced materials, biopharmaceuticals, mobility, life sciences, and electric vehicle (EV) battery sectors, according to the company’s website.