No, the problem is - you can't rob all money in a bank by changing a few numbers in its database. Once the bank discovers it, they'd simply ask the central bank (FRS, ECB, whatever) to roll back fraudulent transactions. That'd probably require quite a lot of phone calls, scrambling for audit trails, court orders - but it can be done.
A real life example - a couple years ago someone tried to do this trick with the Pension Fund of Russia. They've mounted a virus attack on PF's computing system, forcing it to be turned off. Then attackers used faked identity to impersonate a worker of Pension Fund to gain access to Russian Central Bank operations hall and used a forged paper payment order to transfer $30 millions to an account in a small private Russian bank. That payment went through successfully.
However, it was discovered the next morning. Payment was rolled back and police then easily tracked down the attackers.
With bitcoins once your money is stolen - that's it. You can't do anything at all. And even police won't help you, because chances are your attackers are in China or some other nice place with an unfriendly government.