Security
Why app codes beat text messages
Codes sent by text message can be stolen by moving your phone number to someone else’s SIM card. Codes from an authenticator app cannot. What SIM swapping is and how to protect against it.
What a SIM swap is
In a SIM swap, a criminal persuades a mobile operator to move your phone number onto a SIM card they hold, usually by pretending to be you. From then on your calls and text messages go to them, including any login codes sent by SMS.
Why app codes are safer
An authenticator app generates its codes on your phone itself, from a secret stored in the app. Nothing is sent over the phone network, so a stolen phone number gives nobody your codes. That is why fourdigits uses an authenticator app for two-factor authentication rather than text messages.
Protect your number anyway
Ask your mobile operator to add a PIN or password to your account, so nobody can move your number without it. Many operators offer this at no cost. It protects every service that still relies on your phone number, not just one.
Signs something is wrong
If your phone suddenly loses signal for no reason and you receive messages about a SIM change, contact your operator at once from another phone. Then check your email and exchange accounts. Moving quickly limits what a stolen number can be used for.