by Calculated Risk on 1/18/2008 06:15:00 PM

From Christine Richard at Bloomberg: Ambac Insurance Loses AAA Ranking at Fitch Ratings

Ambac ... became the first bond insurer to lose its AAA rating after Fitch Ratings downgraded the company.

Ambac Assurance Corp. was lowered two levels to AA and may be reduced further ... Fitch said today in a statement. ... The downgrade throws doubt on the ratings of $556 billion in municipal and structured finance debt guaranteed by Ambac.
...
The seven AAA rated bond insurers place their stamp on $2.4 trillion of debt. Losing those rankings may cost borrowers and investors as much as $200 billion, according to data compiled by Bloomberg.

Moody's and S&P are also reviewing the bond insurers, see:

S&P: Bond Insurer Review to be Completed Next Week

Moody's: Ambac Under Review for Possible Downgrade