I can't believe that this wasn't foreseen. Bitcoin transactions can be reversed, it happens. It's absolutely irresponsible to not reconcile the block chain against your accounting backend every so many blocks.
This
was forseen:
MyBitcoin is still accepting payments with only 1 confirmation. This is insane for a bank. Any miner capable of mining two blocks in a row can steal money from MyBitcoin pretty easily. I'm surprised no one has attempted it yet.
There's another attack made possible by accepting payments with less than 6 confirmations that would allow you to see exactly which coins MyBitcoin has, and possibly do other damage.
This is not a fault with bitcoin, and bitcoin transactions still can't be 'reversed'. Anyone accepting bitcoins should be waiting for more than 1 confirmation. Sensationalist posts saying 'Bitcoin transactions can be reversed' don't help.
Will