The "hack" that Aravan pulled on the bank a few days ago (that put him way in the negative) was pretty simple. He had two browser windows open and fired them at the exact same time and it let both transactions go through (so the 10 minute wait didn't matter).
While the end result was no gain (or loss), since it essentially just let both transactions process normally, I figured I'd better find a way to stop it before someone found a more "creative" way to use this.
Now, whenever you deposit or withdraw any amount of money, there will be a pause of 1-5 seconds before the transaction goes through. The pause is random, and it's calculated down to the microsecond. This means that your two browser windows will actually not process at the same time, so the second transaction will be denied.
Licensed to Ban
Hahaha sneaky!! brilliant lateral thinking Mickey! That should put a holt on multiple transactions