We've tried to make it as secure as possible. The idea is that the pin is only sent over the call. So the hacker would need to listen in to your call in order to steal your pin. So they basically need to hack your SMS and your voice calls. How else can we make this more secure?
As for publishing your phone number so that you can receive bitcoins, you can publish your secondary phone numbers. We only allow you to use SMS to access your account from your primary phone number, but you can receive funds on any other phone number attached to your account. So even if a hacker knows your pin and is able to fake a call to us from your published phone number, they won't have access to your bitcoins.
As for publishing your phone number so that you can receive bitcoins, you can publish your secondary phone numbers. We only allow you to use SMS to access your account from your primary phone number, but you can receive funds on any other phone number attached to your account. So even if a hacker knows your pin and is able to fake a call to us from your published phone number, they won't have access to your bitcoins.