SIM swap
Moving a phone number onto a different SIM card, legitimately or as an account-takeover attack.
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A SIM swap transfers a subscriber phone number from one SIM card to another. Done legitimately, it is how someone keeps their number after losing a handset or upgrading a device.
Done maliciously, it is one of the most effective account-takeover techniques in use. An attacker who social-engineers a carrier into porting a number onto a SIM they control receives that victim SMS messages, including one-time passcodes, and can then reset passwords on accounts secured by SMS-based two-factor authentication.
This is the main argument against treating SMS as a strong second factor for high-value accounts. Systems that must rely on it often check for a recent SIM change before trusting an SMS passcode.
Related terms and concepts
- Number portability — The ability to keep a phone number when switching from one carrier to another.
- Opt-in — A recipient explicitly granting permission to be contacted by call or text.
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