S&P 500 Leaders & Laggards: Moody's, Sallie Mae

Shares of Moody's Corp. posted the biggest loss on the Standard & Poor's 500 index Wednesday, following a report saying computer errors mistakenly assigned top-quality ratings to debt that declined in value later.

According to the Financial Times, Moody's wrongly gave triple-A ratings to billions of dollars worth of investments known as constant proportion debt obligations because of an error in the rating agency's computer models. Moody's said it is investigating the matter.

Moody's dropped $6.99, or 15.9 percent, to $36.91.

The S&P 500 lost 22.69 points, or 1.6 percent, to 1,390.71.

Bond insurer MBIA Inc. slid 97 cents, or 10.7 percent, to $8.12 as many financial stocks were hit hard in the sell off.

Homebuilder Lennar Corp. declined $1.40, or 7.4 percent, to $17.43 after the Mortgage Bankers Association said mortgage applications fell last week for both refinance and purchase loans, showing continued weakness in the sector.

Among the gaining stocks, shares of student lender SLM Corp., or Sallie Mae, jumped $1.22, or 5.9 percent, to $22, following news the Bush administration will help struggling student lenders by having the government buy up their loans.

Brewer Anheuser-Busch Cos. rose $2, or 4 percent, to $52.65.

Compuware Corp. gained 34 cents, or 3.7 percent, to $9.52.