A SIM-swap attack is when an attacker transfers control of your SIM card to a phone that they control. If you have accounts that use your phone number for 2FA then they can bypass that 2FA security. 

Zengo is perfectly safe against SIM-swap attacks because we never use your phone number. We also have no single point of failure so even if an attacker obtained your email address, phone number, or phone, they still wouldn't be able to access your funds. 

However, you should make sure to enable 2FA on your iCloud account using Authy, 1Password, or a hardware 2FA key. We don't recommend Google Authenticator because it is tied to your device so if you lose your device, you can't access your codes.