If a data breach exposed your phone number, watch for an attempted SIM swap. A SIM swap means an attacker tricks your carrier into moving your number to a SIM the attacker controls. After that move, the attacker's phone gets your calls, texts and data. That access lets criminals go after codes and accounts tied to your number.
Table of Contents
- How a SIM swap hijacks your number
- What are the two warning signs?
- Why are your texted codes the real target?
- What should you do the minute you suspect a swap?
- What protection helps, and where are the limits?
How a SIM swap hijacks your number
Attackers impersonate you to your carrier and ask to activate your number on a SIM they hold. The Federal Trade Commission explains that once the switch succeeds, their phone receives your calls, texts and data, in FTC guidance on SIM-swap scams.
A leaked phone number helps because it tells criminals which number to target. Breached personal details can then help them pass carrier checks and sound convincing.
What are the two warning signs?
The clearest sign is sudden loss of mobile service in a normal coverage area. Your phone may go dark, show No Service, or allow only 911 calls.
The Federal Communications Commission says that change often means your number was swapped or ported out, in FCC guidance on port-out fraud. The second sign is a carrier message you did not expect. Treat any alert about a SIM change, eSIM activation, number transfer, or port-out request as urgent when you made no request.
- Service drops to No Service or emergency-calls-only where coverage is normally fine
- Unexpected text, email, or app alert about a SIM, eSIM, transfer, or port request
- Friends report your number is unreachable while your phone looks idle
Why are your texted codes the real target?
Banks, businesses and payment services send SMS verification codes to prove it is you. After a swap, those codes go to the attacker's phone instead of yours.
Criminals then use intercepted codes to reset passwords and enter email, financial and crypto accounts tied to the number. Anyone relying on SMS two-factor authentication faces the highest exposure, because a swapped number receives both one-time codes and password-recovery messages.
What should you do the minute you suspect a swap?
Act from another phone or a secure connection, because your phone may no longer receive calls or codes. Contact your carrier immediately, then contact banks and other sensitive accounts.
Do not wait to see if service returns on its own. Fast reporting can limit account takeovers and creates records you may need later.
- Call your carrier from another phone and report an unauthorized SIM or port request
- Warn banks, email providers, payment apps and crypto services tied to the number
- File a police report and complaints with the FCC, FTC and FBI IC3
What protection helps, and where are the limits?
The Cybersecurity and Infrastructure Security Agency advises against using SMS as a second authentication factor, in CISA guidance for mobile communications. It recommends authenticator apps, hardware security keys or passkeys, plus a carrier PIN to block unauthorized ports and swaps.
Carrier rules add only a baseline defense. The Federal Communications Commission required carriers, effective July 8, 2024, to use secure authentication and promptly notify customers about SIM and port requests, in FCC notice on SIM-swapping protections. Those checks cannot stop every attack that uses already-breached personal data, so move important accounts off SMS codes now.
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