Segregation of Obscurity

From Forbes account of the Societe Generale billion dollar fraud:

"It's Nick Leeson, the story is exactly the same," said Celent's Pierron. "We have a trader who trades futures, or derivatives, who hides his losses by using weaknesses in the risk-management system." He said that as long as traders had knowledge of back-office operations, the risks of
abuse would always be there.

A spokesperson for Societe Generale said that there would be thorough reviews of internal controls, but noted that this particular case of fraud was "very, very sophisticated."

So, segregate controls, but keep them obscure.