IN THE WORLD of finance, money market mutual funds are about as safe and boring as it gets. They invest customers' money in a diversified portfolio of short-term, highly liquid securities and, in return, provide a modest rate of interest along with bank-like services and access to cash. No problem. Or so it seemed until the financial crisis of 2008 caused a run on money market funds — a sudden outflow of $300 billion in three September days, which forced the federal government to guarantee the funds temporarily.
