I was having a issue with my blockchain account, so I searched for help on Facebook. Then I got a message from some obviously not related to Blockchain (I didn't know this at the time) but acted as their support team and wanting to help resolve my issue. This person requested my blockchain pairing code so he could fix the problem. After providing it to him, all my BTC was sent out of my account. How did he access my account with just my pairing code?