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?
Blockchain.info pairing code allows you to sync wallets. For example, it's for when you have coins on your phone and you want to be able to spend them from your computer. So, they synced their wallet with your account, including the private keys, and stole your coins.
As with your wallet ID, you should never share your pairing code with anyone. The pairing code grants full access to your wallet and its funds. It should be used only by you, when you want to access your wallet on your mobile device.
It is very easy to steal bitcoins using the pairing code. There is a lot of information about that on the internet. In simple words, he has synchronized his wallet with your account and transferred the coins. I am very sorry, you need to be careful next time