If you donate money to Eos, I will give you 5k karma.

The validation they made for me was basically charging a random (low) ammount from your bank account after you put in all information of your card in it. Then they ask you to input on the site that ammount that was charged (as a type of password). Finally they'll validate that the card is yours (they also called me by phone).
This was for a credit card though, dunno if it's any different for prepaid.

That's how my bank account went, too. My credit card I just had to put in the number and expiry date and it works. That being why CCs are not as safe as debit I guess >_> You need to trust the person you give the number to.