Often your phone is the weakest link to all of your online and sometimes offline identity. Someone wrote a detailed and lengthy advisory on how to protect yourself against such attacks.
The security loophole these hackers are milking can be used against anyone who uses their phone number for security for services as common as Google, iCloud, a plethora of banks, PayPal, Dropbox, Evernote, Facebook, Twitter, and many others. The hackers have infiltrated bank accounts and tried to initiate wire transfers; used credit cards to rack up charges; gotten into Dropbox accounts containing copies of passports, credit cards and tax returns; and extorted victims using incriminating information found in their email accounts.
But the hackings should scare anyone with a mobile phone, an email account or an online bank account.
Source: Hackers Have Stolen Millions Of Dollars In Bitcoin — Using Only Phone Numbers