Merger and acquisition news and continued turmoil in the mortgage market shaped some of the biggest business stories this week.

On Monday, shares of Yahoo Inc. soared on news that Microsoft Corp. backed billionaire investor Carl Icahn's effort to oust Yahoo's board, raising the possibility Microsoft may renew its bid to buy Yahoo. In May, Yahoo rejected an unsolicited $47.5 billion takeover offer from the world's largest software maker.

Shares of Yahoo soared $2.56, or 12 percent, to close at $23.91 in heavy trading Monday.

More developments came on Friday as media mogul Rupert Murdoch said it is "very unlikely" News Corp. will get involved, ending speculation that Microsoft was seeking Murdoch's help to break up Yahoo. Murdoch also predicted Microsoft will walk away from the deal in six months.

Shares of Yahoo finished the week 10.4 percent higher.

On Tuesday, shares of mortgage lender IndyMac Bancorp Inc. dropped following news that the company stopped accepting new loan submissions in its main mortgage lending divisions and plans to cut its work force by more than half.

The stock slid 38 percent to end heavy Tuesday trading at 44 cents. They finished the week at 28 cents, down 55 percent from their closing price Monday, the day before the announcement.

Fannie Mae and Freddie Mac were the market's focus on Wednesday amid worries the mortgage finance companies will have to sell more new shares than previously expected because of a slumping housing market.

Fannie Mae and Freddie Mac play a major role in the housing market, and investors are worried they won't be able to withstand losses from foreclosures and home loan defaults.

Freddie Mac shares tumbled 23.8 percent to close at $10.26 Wednesday. They earlier traded at a 16-year low of $9.88. Shares of Fannie Mae fell 13.1 percent to $15.31.

Shares continued to tumble in heavy trading Thursday. Freddie Mac shares fell 22 percent to finish the session at $8. They sank as low as $6.75 earlier in the day. Shares of Fannie Mae fell 13.8 percent, to $13.20. They traded as low as $11.70 earlier.

On Friday, shares of both companies continued trading at levels last seen in the early 1990s, though Treasury Secretary Henry Paulson and President Bush tried to reassure the market about the companies' health.

Freddie Mac's shares plummeted to $3.89 before finishing the day down 3.1 percent at $7.75. Fannie Mae's shares ended the session down 22.4 percent at $10.25, after sinking as low as $6.68 earlier in the day.

On Thursday, Dow Chemical Co. offered to buy Rohm and Haas Co. for more than $15 billion in cash, or $78 per share - a steep premium. The deal would expand Dow's presence in the higher-margin specialty chemicals market.

Rohm and Haas shares soared 64 percent to $73.62 Thursday, while Dow shares fell 4 percent to $32.52.

Shares of Dow on Friday declined 82 cents, or 2.5 percent, to close at $31.70, as Rohm & Haas rose $1.08 to $74.70.

On Friday, shares of Anheuser-Busch Cos. gained after published reports said the brewer will probably accept a sweetened buyout offer from Belgian-based brewer InBev SA as early as this weekend.

The stock jumped $5.29, or 8.6 percent, to close at $66.50.

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