LG Uplus tackles IMSI vulnerability with new SIM card rollout

The company's SIM replacement program addresses a potential security risk posed by a vulnerability in its IMSI system.

The third-largest South Korean telecom operator, behind SK Telecom and KT Corporation, is resolving the issue by replacing physical SIM cards or by providing a SIM card software update via the company website and the U+one app.

The company processed a little bit more than 181,000 transactions on Monday, which was the first day of the SIM replacement program. Of those, 95,986 were SIM updates and 85,023 were replacements of physical SIM cards.

"We are simultaneously operating reservation-based operations and on-site response so that SIM card updates and free replacements can be carried out more smoothly," said Lee Jae-won, LG Uplus vice president of consumer division, in a statement .

"There was a temporary delay on the first day of operation, but we will stabilize the service and minimize customer inconvenience through additional work such as capacity expansion, and apply a stronger security system without any setbacks," he added.

There are concerns that identifiable patterns linked to phone numbers, when combined with external data, could allow third parties to identify or track specific users.

According to The Korea Times , LG Uplus recognized the need to randomize its IMSI scheme after SK Telecom experienced a massive hacking incident in 2025. The company has been preparing countermeasures since the second half of last year.

"This measure is a decision to preemptively strengthen security to ensure that customers can use mobile communication services with more peace of mind, and we will thoroughly prepare to minimize customer inconvenience during the process," Lee said of the SIM card replacements.

Senior Editor, APAC, Light Reading

Gigi Onag is Senior Editor, APAC, Light Reading. She has been a technology journalist for more than 15 years, covering various aspects of enterprise IT across Asia-Pacific.

She started with regional IT publications under CMP Asia (now Informa), including Asia Computer Weekly, Intelligent Enterprise Asia and Network Computing Asia and Teledotcom Asia. This was followed by stints with Computerworld Hong Kong and sister publications FutureIoT and FutureCIO. She had contributed articles to South China Morning Post, TechTarget and PC Market among others.

She interspersed her career as a technology editor with a brief sojourn into public relations before returning to journalism, joining the editorial team of Mix Magazine, a MICE publication and its sister publication Business Traveller Asia Pacific.

Gigi is based in Hong Kong and is keen to delve deeper into the region’s wide wild world of telecoms.