SKT hack: Do I need a new SIM? How do I replace it? Your questions answered.

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SKT hack: Do I need a new SIM? How do I replace it? Your questions answered.

Published: 29 Apr. 2025, 07:00 Updated: 30 Apr. 2025, 14:16

CHO YONG-JUN
[email protected]

Audio report: written by reporters, read by AI

Customers wait outside an SK Telecom branch in central Seoul on April 28 [CHO YONG-JUN]

SK Telecom (SKT) announced April 22 that “customer USIM data was leaked due to malware,” but the company did not disclose what and which sensitive information was leaked, or to whom the information was leaked.

The telecommunication company has not been able to find cases in which the leaked information has been used so far and said it plans to do a full systemwide checkup and strengthen security. But it is currently offering something called “USIM Protection Service,” free of charge, to all customers, as well as a free SIM replacement to anyone who wants some peace of mind.

If you're an SKT customer, should you be waiting in front of a store to get your SIM card changed today, or be worried about your bank account being hacked? Here's what experts say.

What does this SKT data breach mean for my phone data? Should I be very afraid?

We don't have a ton of information other than what the company announced. In a worst-case scenario, whatever suspicious characters received the USIM data of SKT users might be able to create a copy of those users' SIM cards with an identical phone number. In that scenario, they could use that cloned SIM card to call people, purchase things, log into banks — the various things you do with your personal phone number.

What are the chances of that actually happening to your SIM card? Very low, according to KAIST cybersecurity Prof. Kim Yong-dae.

Kim explained that when — and if — a hacker were to duplicate your SIM card, they would then need to connect that duped card to the SK Telecom network. Since only one version of any given SIM card can be on that network, the two SIM cards would “fight” each other to connect. Most likely, SKT would figure out that this was happening before too long, suspect that a SIM card had been cloned, and cut both of them off.

“The real user will also be in an inconvenient situation,” Kim said. “But at least it also prevents the hacker from connecting.”

But that only applies if your phone is turned on. If your phone happened to be off when a hacker attempted to access a network with a duplicated SIM card, SKT wouldn’t necessarily know that it was a duplicate, which could give the hacker free rein.

Should I replace my SKT SIM card?

Yes, you should get a new SIM card — if they’re in stock.

“The encrypted keys and data have been leaked; it is still recommended,” says Kim.

A notice about USIM replacement reservations is posted at an SK Telecom retail store in Seoul on April 28 as the company begins offering a free USIM replacement service following the hacking incident involving customer information. [YONHAP]

How do I replace my SIM card?

As of press time, SIM cards are largely out of stock at SK Telecom's branches, but you can join the waitlist on SKT's website. If you sign up for this, you'll get a text the next time a new SIM card is available.

To sign up, you'll need to enter your legal name, identity card or ARC number and phone number. You'll also want to have the name or address of your nearest SKT store on hand. We have a more detailed step-by-step guide to help you with the exact sign-up process if you can't read Korean well.

SKT told the Korea JoongAng Daily on Wednesday that it is "looking to support" English and other languages for its SIM replacement website.

"Meanwhile, we recommend users to use Chrome or Safari's translation features."

In the meantime, it is worth signing up for SKT's USIM Protection Service, which can offer protection for the time being.

Can eSIM users also get their eSIM replaced?

Yes, but you still have to go to the store.

Can prepaid users get their SIM replaced?

Yes, and prepaid users can also sign up for the SKT USIM Protection Service.

What is the SKT USIM Protection Service? Is it actually useful?

SK Telecom’s USIM Protection Service aims to protect you from fraud if your SIM card is compromised.

Signing up and turning on the USIM Protection Service will outright ban your SIM card from working on phones that are not your phone, meaning that even if a hacker duplicates your SIM card, it won't work.

“Theoretically, there is no loophole with USIM protection service,” the professor said.

The USIM Protection Service, however, will also block you from using overseas roaming, so it's not a good long-term solution. If you need to travel abroad while enrolled, your best solution is a separate data-only eSIM — which is also often cheaper. You also, of course, cannot swap your SKT SIM to another phone if you have this on. But, again, this USIM Protection Service is only meant to be a short-term solution.

How do I sign up for the USIM Protection Service? Does it cost money?

USIM Protection Service is free for SKT members. You can sign up for it on the T World website. There may be a queue, though there is not one as of press time.

If I get a new SIM, do I need to change my phone number? Will it delete all my apps, photos and other data?

No, and no. Unless you want to change your phone number, swapping your SIM will not automatically give you a new number.

Your photos and applications are stored on your phone, not on your SIM card; those will stay on your phone when you swap your SIM. However, some owners of Android phones may have their contacts saved directly to their SIM card — these people will have to first transfer them from their SIM cards to their phones before swapping. (If you are someone who needs to do this, you probably know.)

Some bank apps that require you to save authentication data directly to your phone may require you to re-authenticate when you receive your new SIM card.

Can I get a replacement SKT SIM card without visiting the store?

No. SKT only does SIM replacement in its branches, ostensibly to "reassure" customers. If you’re considering moving to a different carrier, however, it is possible to cancel an SKT plan without visiting a branch.

I got the text! Anything else I need to do before heading to the store?

Don't forget to bring your phone, your current SIM card and ID to the store.

Android users who have prepaid transportation cards on their phones will also have to get their remaining balance refunded before they can make the swap. Check your transportation card app or contact the transportation card provider for further assistance with this.

BY CHO YONG-JUN [[email protected]]