The New York Times fingers hedge fund manager William Ackman for yesterday's down market. That's because Ackman has been a vocal pioneer of the idea that bond insurers lack the capital to back their bets on the solvency of the bonds they insure and they might lose $24 billion as a result. And the holders of those bonds are banks and insurance companies which will be forced to write-down the value of those bonds -- to the tune of $70 billion more -- if the bond insurers lose their AAA ratings.

I wrote about Ackman's bet against bond insurance last May. If you had followed my suggestion to follow Ackman's short sales of MBIA (NYSE: MBI) and Ambac Financial Group (NYSE: ABK) you would have profited from the respective 81% and 89% declines in these stocks since then. And as a protege of Harvard Business School Professor Michael E. Porter -- with whom I worked -- I admire Ackman's analytical skills and his willingness to put money into his bets. Moreover, Ackman pledged to give the profits from his bond insurance short sales to charity.

But Ackman's estimate of the losses from downgraded bond insurers is big and scary. His report yesterday predicted that MBIA and Ambac might lose $24 billion on the CDOs they guaranteed. That $24 billion is a significant percentage of the $1 trillion in municipal, corporate and mortgage debt that they insure with their AAA ratings. Unfortunately, ratings agencies like S.& P. and Moody's Investors Service may downgrade them due to a lack of capital relative to their potential losses.