Unless you can get the cash and run away (far far away), whatever you do with the money will be cancelled by the bank and the international bank association as soon as they discover the mistake (i don't know it's name but i know there is one). They can do it easily since they can prove very easily the mistake.
If they don't notice it, the legal procedure in my country is that you have to declare it to the police, and if nobody claims it for three years it's yours.
I would probably have not told anything and taken a picture of my screen every day to see how long it takes them to notice. Shouldn't be very long, bankers have automated software that monitor bank accounts and trigger notices so that your local bank manager can present you with the bank services if you have funds.
Desktop : Intel Core i5-750, 4GB RAM, ATi HD5870, Windows 7 64bit
Laptop : Intel C2D-P8600, 4GB RAM, nvidia 9700M-GT, Windows Vista 64bit
Displaying Zalman Trimon 22" and 106" Passive polarised dual projector setup.
Watch my Stereo3D gaming video footage viewtopic.php?f=3&t=2020