How many folks, do you suppose, woke up with a start last week and decided that they'd sleep better if they switched their savings from uninsured money market funds back to federally insured savings accounts? For the first time, a money market fund had collapsed, giving investors only 94 cents for every dollar that they had put in.

Derivatives were at play, and the collapse of a money market fund sent a shiver through the financial world. Derivatives had hurt at least 15 other funds, but advisers had pumped in more than $650 million to maintain their value. Last week, the Community Bankers U.S. Government Money Market Fund decided not to inject more money but to shut down and liquidate. It was the first time a money market fund had, as the phrase in the fund game goes, "broken the buck."

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