Lesson 14 of 14 · About 4 minutes
Lock your number against SIM swaps
Learn the concept.
Your phone number can move to another SIM or eSIM without your phone being stolen. If a scammer gets the carrier to reroute it, calls and text-message codes may reach their device instead.
An unexpected alert. A route you can trust.
Follow the sequence, or move one step at a time.
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Read all 4 steps
- A change Leo did not request
Leo pauses when the notice arrives. He does not use the message’s link or share his account PIN.
- Open the carrier independently
He uses the official app or a trusted support contact and reports the unauthorized change promptly.
- Check what the protections cover
He asks about both SIM-change and number-transfer protection. If the change completed, he needs recovery help.
- Reduce reliance on text codes
After resolving the number issue, he checks affected accounts and chooses stronger supported sign-in and recovery methods.
The number moves. The texts follow.
Illustrative SIM-swap risk: an attacker persuades a carrier to move your mobile service to a SIM or eSIM they control.
- Your account sends a code
A service sends a sign-in code to your mobile number.
- The carrier routes the number
An unauthorized SIM change redirects new calls and messages.
- The wrong device receives it
The attacker may receive the text while your own phone loses service.
Read the visualWhy does an authenticator app help with this particular risk?
Its codes are not delivered to your phone number by SMS. You must still protect the app, its recovery methods, and the codes from phishing.
Know which change you are protecting
A SIM swap moves service to another SIM or eSIM. A fraudulent port-out moves your number to another carrier. Providers may offer separate protections for these changes, so ask about both. A phone screen lock does not secure the carrier account that controls the number.
Set protection before an alert arrives
Use your carrier’s official app, website, or trusted support contact to set a strong account PIN and review available SIM-change and number-transfer locks. Names, eligibility, and coverage vary. Confirm what each control protects; do not assume one “number lock” blocks every kind of change.
Choose sign-in methods that do not rely on texts
Where supported, an authenticator app avoids delivering sign-in codes through your mobile number. App codes can still be phished; never give them to an unexpected caller or message sender. Passkeys or FIDO security keys offer phishing resistance. Keep a secure recovery method, and do not turn MFA off if text codes are the only available option.
Treat an unexpected change as urgent
An unrequested SIM-change notice or sudden loss of service needs checking, although an outage alone is not proof of fraud. Contact the carrier independently, using another connected device if needed. Ask them to stop or reverse unauthorized changes. Once control is restored, secure affected accounts and review them for changes or unfamiliar activity.
Put it in context
In the fictional Day 16 Short, Leo receives a SIM-change alert he did not request and locks his number before the transfer finishes. In our practice, the next move is to open the carrier’s official app independently and report the request. The alert is a reason to act promptly, not a reason to trust a link inside the alert. A completed transfer may require the carrier’s help to reverse.
Make a decision.
Use what you just learned. A correct answer lets you save this lesson to your progress.
Take this with you.
Protect your carrier account, ask about SIM-change and number-transfer locks, and check unexpected alerts through a trusted carrier route.
Explore a career trackContinue with passkeys and phishing resistance or protecting your recovery codes.
See it in a Short.
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