Hackers gain access to your bitcoin from your cell phone in what's known as a sim card swap attack.

I have briefly read about what is known as the sim card swap attack. This is fairly easy to explain - The hacker uses social engineering to persuade the employee at your local cell phone store or over the telephone to replace the sim card to the hackers cell phone thus making all calls and texts of your phone number go to him. The hacker can then use your two factor authentication at coinbase, bitfinex and every other place that you might store bitcoin on.

Tips so this wont happen to you. Use a hardware wallet to store your bitcoin. Use two factor authentication on every single place where it is available. Use different passwords that are long for every website. Passwords nowadays should not look like this: Njs*&&#$GDhbfn It was recently stated that a password with random words is harder to break such as CatMOses..HealFriend82(#98 As it takes brute force hackers a lot longer to decypher. If you don't know what two factor authentication is please look it up on google. Every online wallet you use has a security section and that security section is your best friend go to it and learn everything you can about it such as IP whitelisting. New browser confirmation. Email confirmation on withdrawals.

Best Wishes