Shares of Bermuda-based bond insurer Assured Guaranty Ltd stabilised on Friday after the announcement that its ratings would be reviewed by Moody’s sent its shares plunging more than 13 percent in midweek.Moody’s may cut the Aa3 rankings of Assured’s insurance units, Assured Guaranty Municipal Corp, Assured Guaranty Corp and their affiliated insurance operating companies, the New York-based ratings company said in a statement.Assured CEO Dominic Frederico responded by describing Moody’s actions as “unjustified and unwarranted”.Standard & Poor’s lowered Assured ratings two steps in November to AA-, a level that’s equivalent to Moody’s current ratings.On Wednesday, Assured’s shares fell 13.4 percent to $16.30, the biggest drop since August 8, according to data compiled by Bloomberg.On Friday, the shares closed on $16.30 in New York trading.“We have been working with Moody’s for some time, emphasising the improvements in our credit profile since their last review in 2009,” Mr Frederico said.“As the current rating process is not yet complete, we are surprised that Moody’s decided it had enough information to place Assured Guaranty on review for a possible downgrade.“In light of our improved financial strength over the last two years, Moody’s action was unjustified and unwarranted. Assured Guaranty has not just, as Moody’s writes, ‘survived’ the financial crisis but has demonstrated its resiliency, resourcefulness and financial strength, while we have paid nearly $4 billion in claims since the onset of the mortgage crisis.“Since our last rating assignment, we have achieved record operating income.“Our business production continues to demonstrate a fundamental demand for our product.“We believe we are firmly in the Aa rating category.”Moody’s cited lower origination volume and reduced demand for the bond insurer’s business, economic stress in the US and Europe related to mortgage and municipal finance and pressure on operating margins with interest rates at about record lows.Assured has recorded a return on equity of 14.9 percent in 2010 and 12.1 percent in 2011, Frederico said in the statement.It has insured more than $58 billion of US municipal bonds since that time and it has captured one out of every eight new issues last year, he said.Assured recorded net income of $775.6 million in 2011.