We suggest that you should enable 2FA (Two-Factor Authentication) in your account, so as to make it more safe and ensure the security of your funds
In order to do so you have to download "Google Authenticator" on your phone via App Store or Android Market.
To finish up, enter your login, password and the 6-digit number in "Google Authenticator".
Then scan the QR code or manually add an account in Google Authenticator (enter the 16-bit key over the QR code).
Now you can use it!