"As an investor," he says, "I'd want to know: What kind of system do you have in place to prevent individual traders on single desks to expose you to such a huge number on the downside that it wipes out your entire third quarter's profits?"

Here, UBS's recent track record on risk management comes to bear.  Investors buy securities based on public information and what the company says to the market.  Since Gruebel came aboard, "the bank has been saying, We're serious about risk, we're serious about righting the ship," says Auld. But the news of the rogue trading prompts investors to wonder: "Was management really being honest?"