What Is SIM Swapping? The SMS Trap That Empties Crypto Accounts

SIM swapping is when someone persuades your mobile network to move your phone number onto a SIM card they control. From that moment every call and text meant for you arrives on their phone, including the password reset links and the six-digit codes that guard your exchange account. Victims usually notice when their own phone quietly loses signal, which is often far too late.

How does someone take over your number?

Rarely by hacking anything. They call the network pretending to be you, say the phone was lost, and answer the security questions with details scraped from a data breach or your own social media: date of birth, address, the last few digits of a card. Sometimes they simply pay a shop employee. The number is the front door of your digital life, and it is protected by a customer service script.

Why are SMS codes the weak link?

Two-factor authentication by text is only as strong as your phone company. Once the number moves, the thief clicks "forgot password" on your email, receives the code, takes the email, and then resets the exchange account that email controls. Some of the largest personal crypto thefts on record began exactly this way, with no malware and no stolen seed phrase.

What actually stops it?

• Drop SMS for two-factor. Use an authenticator app, or better, a hardware security key. On any exchange that offers both, switch and then remove the phone number.
• Add a port-out PIN with your carrier. Most networks offer a number transfer lock or a separate passcode. Ask for it by name.
• Use a separate email for crypto that you have never posted publicly, with its own strong password.
• Keep long-term holdings off exchanges entirely, on a device you control.

Do the carrier lock this week; it takes one phone call and it is the step almost everybody skips. And if your phone suddenly loses service for no reason, treat it as an emergency: get to another device, change your email password, and lock your exchange accounts before you go looking for the cause. For the bigger picture on custody, read not your keys, not your coins and our guide to hardware wallets.