Standard & Poor's revised PMI Mortgage Insurance Co.'s (PMI) credit and financial strength ratings to R from CCC- Tuesday, while also placing the mortgage insurer on a negative credit ratings watch. The change arrived after the insurer said it would no longer be able to write new business in any state and is now under the direct supervision of its primary regulator, the Arizona Department of Insurance. A rating of "R" is very close to the bottom of S&P's ratings scale. Based on S&P criteria, the R rating is given when a firm is "under regulatory supervision owing to its financial condition." S&P says in this situation, the R rating lets investors know regulators have "the ability to favor one class of obligations over others or to pay some obligations and not others" when making financial decisions. August has been rocky for PMI Group. The company's stock fell more than 50% during a volatile trading day in early August. The firm also received a delisting warning from the New York Stock Exchange after the mortgage insurer's stock closed at less than $1 for at least 30 consecutive trading days. Write to: Kerri Panchuk.