A friend of mine told me an interesting story. A trader in bank X tried to make a profit, building a private portfolio with some new financial product and using bank's money. Apparently, he abused his position and connections within the firm in order to do so. The sad part of the story is, that he ended up playing against bank Y and loosing half of the cash. Obviously, he wasn't an exceptionally bright trader and also no proper pricing model was available for that particular product/portfolio.
Shortly after the loss the worst happened - bank Y bought bank X. Now in full control, they sent investigators in order to uncover the whole story and punish the guy. So now he faces criminal charges against him, and maybe will spend some time in prison.
Just to remind you - Nick Leeson caused the collapse of the Barings Bank in the 90ies.