What happened to mt gox and bitcoin sounds more like virtual bank robbery; comparable to hijacking an armored truck of gold and replacing it with fake gold.
Its more of. I am gonna store 1000 gold bars with you in your vault. Then one day you schedule to come pick up the 1000 gold bars at 12:30PM. Instead you have a duplicate (fake) truck come at the designated time and pick up your gold bars and your truck shows up 5 minutes late.
Then the next day you head over to the bank and say you never received your gold! At which point the bank says they already sent out your gold but you have proof you never received it and they allowed a fake entity(malleable tx) to transport it.