A major data breach at SK Telecom exposed 27 million user records, surpassing its reported customer base of 25 million and becoming one of South Korea’s largest telecom security incidents.

Investigators found 23 of 30,000 SK Telecom servers infected with 25 types of malware, leaking 9.82GB of data, mostly comprising International Mobile Subscriber Identity (IMSI) records vital for mobile authentication.

About 290,000 International Mobile Equipment Identity (IMEI) records were also leaked, raising concerns about potential USIM cloning and cybercrimes.

Two of these servers contained personal information such as names, birthdates, phone numbers, email addresses, and IMEI numbers.

The malware likely infiltrated systems between June 2022 and December 2024, but no signs of further leaks were found between December 2024 to April 2025.

SK Telecom disclosed the breach on April 22, 2025, four days after detection, and has been urged to enhance security measures.

SK Group Chairman Chey Tae-won has issued a public apology regarding the incident.

🔗 Source: The Korea Times

🧠 Food for thought

1️⃣ South Korea’s recurring pattern of large-scale data breaches

The SK Telecom breach continues a troubling pattern of massive data security incidents in South Korea’s digital ecosystem.

In 2011, the country experienced what was then its largest online data breach when hackers compromised 35 million user accounts from Nate and Cyworld, affecting personal information including names, phone numbers, email addresses, and resident registration numbers 1.

That incident was attributed to hackers allegedly traced to China, causing SK Communications’ stock to drop nearly 6% and raising significant national security concerns 1.

South Korea’s position as one of the world’s most digitally connected countries has made it vulnerable to cyber attacks, with several major breaches affecting millions of users over the past decade.

The recurring nature of these incidents highlights the persistent challenges in securing personal data despite technological advancements and increased awareness of cybersecurity risks.

2️⃣ Long-dwelling malware represents a growing cybersecurity challenge