By Kwanwoo Jun

South Korean conglomerate SK Group's chief has apologized for a data breach at its mobile-service affiliate, SK Telecom, which is still reeling from a cyber attack last month.

Shares of SK Telecom, the largest wireless carrier in South Korea, were 1.1% lower, falling for a second consecutive session and taking their total loss to nearly 10% since the company confirmed the cyber attack on April 22, four days after its initial detection of malicious sofware in its network for around 24 million users.

"The recent cyber breach of SK Telecom has caused much anxiety and inconvenience to customers and the public," Chairman Chey Tae-won said in a statement Wednesday. "On behalf of the SK Group, I would like to offer my sincere apologies."

Chey promised to conduct a sweeping data security review on all group affiliates as well as SK Telecom, establish a new data-protection panel involving outside experts and work out a comprehensive solution to enhance security.

No damage related to the latest data compromise has been reported yet, as investigations are still underway to determine who was behind the cyber attack.

Since early last week, SK Telecom has had all its subscribers replace their Universal Subscriber Identity Module cards on mobile handsets for free, in order to prevent any possible illegal use of USIM cards, but progress has been slow due to limited USIM-card supplies. The company has temporarily suspended new subscriptions in order to focus on ongoing USIM-card replacements.

SK Telecom customers have been encouraged to sign up for better data protection services while awaiting their USIM-card replacements, but some impatient and anxious clients have begun defecting to other rival wireless services instead, according to market analysts.

Citigroup in a recent note downgraded its rating on SK Telecom to neutral from buy, citing the company's pause in new subscription services and a rise in additional business costs.

Write to Kwanwoo Jun at kwanwoo.jun@wsj.com

(END) Dow Jones Newswires

May 07, 2025 03:02 ET (07:02 GMT)

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