Ambac Financial and MBIA Inc. plunge on Moody's downgrade warning

Thanks to a downgrade warning from Moody's, bond insurers Ambac Financial Group (NYSE: ABK) and MBIA Inc. (NYSE: MBI) are sitting out today's massive rally in financial stocks. Late Thursday, Moody's announced that it may downgrade the duo's ratings by more than one notch due to rising losses from subprime mortgage debt. So far today, the news has prompted a 7% drop in MBIA shares, and a slump of nearly 8% for Ambac.

In a statement, Moody's said, "Because both Ambac and MBIA are meaningfully exposed to the risk of U.S. subprime mortgages and other residential mortgage products, the revised assumptions are expected to have a significant impact on the firms' capital positions and multi-notch downgrades are possible." Specifically, the "A2" insurance financial strength rating of MBIA's insurance unit is under review, as is the "Aa3" insurance financial strength rating for Ambac.

Neither bond insurer seems particularly pleased by Moody's decision. Jay Brown, chairman and CEO of MBIA, said that the review reflects "inherent flaws" in the ratings company's logic, and added that his company has a capital cushion of more than $3 billion. Ambac's chairman and chief executive, Michael Callen, noted his "surprise and disappointment" at the news, and added that "Moody's ratings actions continue to cause confusion, uncertainty and the risk of material economic damange if their assumptions ultimately prove to be too onerous."

Despite today's plunge, MBI and ABK remain poised atop support from their respective 10-week moving averages. Both bond insurers have endured massive price plunges amid subprime-related fallout, but they've recently rebounded. Ambac now boasts a 60-day relative-strength reading of 381% versus the S&P 500 Index, while MBIA's is 312%.

Elizabeth Harrow is an analyst and financial writer in the research department at Schaeffer's Investment Research. She is featured in the video series Schaeffer's Daily Q&A on SchaeffersResearch.com.