Market participants' measure the default risk of an issue on the basis of the credit ratings that the credit rating agencies assign to the issues. Once rating is assigned, the agency continuously monitors the credit quality of the issuer and updates the ratings from time to time. Rating agency is empowered to either upgrade or downgrade the ratings. An unexpected downgrade increases the credit spread and a fall in the bond's price. The risk involved here is the downgrade risk and is closely related to credit spread risk.