South Korea's largest telecom operator, SK Telecom, suffered a malware attack on April 19, 2025, resulting in the leakage of USIM (SIM card) data of millions of customers. The company initially delayed reporting the cyber intrusion for over 40 hours, which has led to regulatory scrutiny and potential fines. SK Telecom has faced criticism from users for not promptly notifying customers about the breach. In response, the company announced it will offer free USIM replacements to all its subscribers starting April 28, 2025, and will reimburse customers who had already replaced their USIM cards at their own expense. The Ministry of Science and ICT and the Korea Internet & Security Agency are investigating the incident and have pledged to strengthen oversight of major telecommunications providers. Cryptocurrency exchange Bithumb, which could be indirectly affected due to the compromised telecom infrastructure, has also enhanced its security measures following the breach. SK Telecom's CEO Yoo Young-sang apologized for the incident and emphasized that the delay in reporting was due to the need for a thorough investigation rather than intentional concealment.