Under SEC rules, money market managers must invest in securities with “minimal credit risks.” Joseph Mason, a finance professor at Drexel University in Philadelphia and a former economist at the U.S. Treasury Department, says subprime debt in money market funds is far from safe. “This creates tremendous risk for today’s money market investors,” says Mason, who wrote an 84-page report on CDOs this year. “Right now, I’m not comfortable investing anything in CDOs.”