A statement posted on the Vanguard Group's Web site said that the company's chairman John Brennan told CNBC that Vanguard had received "many calls" from investors who wanted to know if their money is safe. Brennan sought to reassure them through the statement that, indeed, it was.

"Clearly, nothing quite like these incidents has occurred before," the statement reads. "But this nation, its people and its financial markets have overcome many challenging events in the past ..."

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