http://en.wikipedia.org/wiki/Moody's
gave Freddie Mac's preferred stock an investment grade rating of A1 until August 22, 2008 when Warren Buffett said publicly that both Freddie Mac and Fannie Mae had tried to attract him and others. Moody's changed the credit rating on that day to Baa3, the lowest investment grade credit rating. Freddie's senior debt credit rating remains Aaa/AAA from each of the major ratings agencies Moody's, S&P, and Fitch.‏⁶