As of the year 2000, Moody's, one of the five leading credit rating agencies for long term corporate bonds (the other are Standard and Poor's, Fitch Ratings, Dominion Bond Rating Service and A.M. Best.), issued a coverted "investment grade" bond rating to about 2,900 companies, and a "speculative-grade" bond rating (the less charitable name for them is "junk bonds" and more charitably called "high-yield debt") to another 5,000.
When an issuer goes from investment grade status to speculative grade status, it is called a "fallen angel." As of February 2009, S&P identified 75 issuers at risk of becoming fallen angels. These bonds must often be sold in a fire sale by institutional investors prohibited from owning speculative grade bonds.