The Ambac Financial Group, Inc., generally known as Ambac (originally the American Municipal Bond Assurance Corporation), is an American holding company. Its subsidiaries provide financial guarantee products such as bond insurance to clients in both the public and private sectors globally. Ambac Assurance is a guarantor of public finance and structured finance obligations. Its common stock and common stock purchase warrants are listed on the NYSE under the symbols and respectively. Ambac is regulated by the insurance commission of Wisconsin. It has its headquarters in Lower Manhattan, New York City. Ambac Financial Group's subsidiaries include Ambac Assurance Corporation and Everspan Financial Insurance Company. History and Credit ratings Ambac, originally American Municipal Bond Assurance Corporation, was founded in 1971 in Milwaukee, Wisconsin as a subsidiary of MGIC Investment Corp. to insure the principal and interest of municipal bonds against default. In 1985, Citibank (the principal subsidiary of Citicorp) acquired majority control of Ambac Inc., parent company of AMBAC. Other investors, including Xerox Corp., Ambac management, and Stephens Inc., an investment banking firm, held the remaining equity. In 1989, Citibank gained sole ownership of the municipal bond insurer, purchasing the remaining shares it had not already secured from its former partners. Citibank, trying to exit the business initiated the IPO of Ambac in 1990 and sold all its remaining shares in the Company in February 1992. In 1997, the company changed its name to reflect its expansion into new areas of business. Ambac Inc. was renamed Ambac Financial Group, Inc. The municipal insurance subsidiary was renamed Ambac Assurance. Ambac and other bond guarantors such as MBIA were hit hard by the 2007 subprime mortgage financial crisis and on January 18, 2008, its Fitch credit rating was lowered from AAA (the highest) to AA when its plans to raise two billion dollars in new capital failed. Moody's and S&P, however, chose to affirm Ambac's AAA with their agencies after it succeeded in raising $1.5 billion in new capital in March 2008. In early 2008, the spectre of the major bond guarantors failing to be able to pay off insurance claims on a trillion dollars of securities backed by sub-prime mortgages and other securitized debt led to attempts to shore them up with infusions of capital. On June 19, 2008 Moody's downgraded Ambac's credit rating three notches to Aa3. Ambac's ratings continued to decline during 2008–2010. Moody's Investors Service lowered the rating of the