https://www.theverge.com/2017/9/18/16328172/sms-two-factor-authentication-hack-password-bitcoin

For a long time, security experts have warned that text messages are vulnerable to hijacking — and this morning, they showed what it looks like in practice. A demonstration video posted by Positive Technologies (and first reported by Forbes) shows how easy it is to hack into a bitcoin wallet by intercepting text messages in transit.

The group targeted a Coinbase account protected by two-factor authentication, which was registered to a Gmail account also protected by two-factor. By exploiting known flaws in the cell network, the group was able to intercept all text messages sent to the number for a set period of time. That was enough to reset the password to the Gmail account and then take control of the Coinbase wallet. All the group needed was the name, surname and phone number of the targeted Bitcoin user. These were security researchers rather than criminals, so they didn’t actually steal anyone’s bitcoin, although that would have been an easy step to take.