A 20-year-old American allegedly used an increasingly popular “SIM swapping” technique to gain control of targeted phones, mainly those owned by cryptocurrency investors, and steal over $5 million in cryptocurrency and other information. The technique requires convincing a mobile provider like AT&T or T-Mobile to transfer a number to another SIM card controlled by the hijacker, who can then use the number to reset email passwords, even when protected by two-factor authentication, and access cryptocurrency accounts. 

Source: ‘TELL YOUR DAD TO GIVE US BITCOIN:’ How a Hacker Allegedly Stole Millions by Hijacking Phone Numbers – Motherboard