Dutch bank to enable money transfers via Facebook and text messages

The Dutch bank Knab announces a new service dubbed 'Knab Social' to transfer
money from a customer's bank account using Facebook or the contacts list in
their phone. The bank's website at https://www.knab.nl/mobiel-betalen
(sorry, Dutch only) explains how it works:

  "Did your friends advance a dinner for you?  Soon you can pay them back
  quickly via Facebook or a text message. Simply using your Knab App.
  Handy, because you don't have to ask them for their IBAN!

  How does it work

  1. Select a friend via Facebook or your mobile address book.
  2. Your friend receives a message that you want to pay money to him.
  3. Your friend enters his IBAN and receives the money."

What would you do if you receive a message that promises you money, if only
you provide your own bank account details?

What do you do when some rogue software decides to send a 'Knab Social'
message to all your contacts, as a Christmas present, emptying your account
in the process?

In other words: what could possibly go wrong?