It is absolutely impossible, that somebody in a position like Jerome Kerviel can hold trading positions for 50 bn Euros and burn 10% of that amount. It is impossible, because

  • banks nowadays would never rely on simple password protection for their trading systems.
  • they all have state-of-the-art identity management in place and manage business roles in a way that one single trader could not crash the whole bank
  • such big deals would always be routed through acknowledgement processes where duties are segregated
  • Strong Authentication techniques and strict authorization would let all employees of a bank feel, that it is impossible to operate with multiple identities falsifying acqunowledgement processes
  • risk dashboards would turn red and start screaming long before such a damage occurs
And, just to be complete: no, it is not possible to attack PIN/TAN online banking transactions, ATM Cards cannot be falsified and it never rains in Hamburg.