This excerpt taken from the ALL 10-Q filed Oct 31, 2007.
Alt-A mortgage-backed securities include certain securities that are collateralized by residential mortgage loans issued to borrowers with stronger credit profiles than sub-prime borrowers, but who do not qualify for prime financing terms due to high loan-to-value ratios or limited supporting documentation. At September 30, 2007, the Alt-A portfolio had net unrealized losses of $10 million, which were comprised of $8 million of unrealized gains and $18 million of unrealized losses. At June 30, 2007, these securities had net unrealized losses of $5 million, which were comprised of $2 million of unrealized gains and $7 million of unrealized losses. $734 million or 55.0% of these securities were issued during 2006 and 2007. During the third quarter of 2007, we opportunistically acquired $233 million of Alt-A securities below par, which are rated Aaa, and separately sold $72 million of Alt-A securities recognizing a loss of $1 million.