The concept of "risk-free" debt is being questioned after Standard & Poor's revised its outlook on the credit rating of U.S. government debt. Government debt has long been considered a safe harbor for investors, but that is changing. "Government bonds have assumed characteristics typical of credit products, for which prices mainly provide measures of borrowers' probabilities of default," wrote Jose Vinals of the International Monetary Fund. "During phases of risk aversion, they do not benefit from flight-to-quality flows. On the contrary, they correlate with risky assets."