The Master Key system was removed with today's update. There were several reasons for this decision. The most important one is that we think smsTAN is a far more secure system, while it is less confusing and much easier to use. We recommend anyone to enable this feature. It's completely free.
No more privacy concerns with smsTAN:
To make smsTAN, our two-factor authentication system for withdrawals, even more attractive, we now encrypt all phone numbers with the account password. For encryption we use the Rijndael algorithm (AES) with a 128 Bit key. This means that your phone number remains private even if our systems are compromised. If you are already using smsTAN your account will be automatically upgraded to the new system once you perform a withdrawal.
Redundant SMS gateway:
We noticed that sending SMS messages is far from stable and often fails for unknown reasons. Therefore we now use two independent gateway providers to make smsTAN more reliable. If SMS messages are not received properly, you can switch to an alternative gateway in the account settings.