Shares of SK Telecom tumbled on Monday, falling as much as 8.5% during trading to reach their lowest point since August 2023, following the disclosure of a significant customer data breach. The stock ultimately closed down 6.7%, marking the company's largest single-day drop since March 2020, even as South Korea’s broader KOSPI index edged up by 0.1%.

Pl pp. UK jykgkgkĥhĥĥ's largest mobile carrier revealed that it had suffered a large-scale leak of customer information earlier this month due to a cyberattack involving malware. The breach was detected on April 18, though the company has yet to release detailed information about the specific nature of the compromised data or the extent of the damage.

In a statement, SK Telecom pledged to take full responsibility for any harm customers may experience as a result of the incident. As part of its response, the company announced it would offer free universal subscriber identity module (USIM) card replacements to all 23 million of its users, available at more than 2,600 retail stores across the country starting Monday.

Additionally, SK Telecom is encouraging customers to enroll in its USIM Protection Service, which the company says offers security measures comparable to replacing a USIM card. As of Sunday, approximately 5.54 million subscribers — nearly a quarter of SK Telecom's customer base — had already registered for the service.

The breach and the subsequent sharp fall in share price highlight the growing risks companies face from cybersecurity threats, particularly in a market where consumer trust is critical. SK Telecom’s handling of the incident will be closely watched as it works to mitigate the fallout and restore confidence among users and investors alike.