Ackman has challenged the strength of MBIA and other bond insurers for more than five years and as recently as November forecast they would be insolvent by the second quarter because of their exposure as guarantors to billions of credit derivatives products packed with subprime mortgage debt.

FORBES: Bond Insurers Need Help--Fast

Before the monolines ran into trouble with exposure to credit derivatives and structured products in late 2007, they enjoyed a robust business insuring municipal debt.

FORBES: Magazine Article

But dealers in credit derivatives have lately been keen to make their products more reliable.

ECONOMIST: Credit derivatives: Rites of passage | The

In recent years, Ambac, MBIA and others have ventured into insuring credit derivatives and other relatively newfangled fixed-income products invented by and peddled by Wall Street.

FORBES: Magazine Article

American International Group shares dropped nearly 6% Thursday on speculation it faced potentially large write-downs of investments in credit derivatives as well as exposure through its financial products group, which sells bond insurance.

FORBES: Merrill Under Fire

In recent years, Ambac, MBIA (nyse: MBE - news - people ) and others have ventured into insuring credit derivatives and other relatively newfangled fixed-income products invented by and peddled by Wall Street.

FORBES: You Should Worry About Ambac