The Federal Reserve Bank of New York said Monday it has begun purchasing mortgage-backed securities in an effort to bolster the battered housing market. The program, initially announced Nov. 25, allows the Fed to spend $500 billion to buy mortgage-backed securities guaranteed by mortgage giants Fannie Mae and Freddie Mac and another $100 billion to directly purchase mortgages held by Fannie, Freddie and the Federal Home Loan Banks.

Borders Group Inc ., the money-losing U.S. bookstore chain that tried to sell itself last year, replaced top management after holiday sales fell 12 percent. Ron Marshall, who ran private-equity firm Wildridge Capital Management for the past three years, was named chief executive officer, replacing George Jones. The company also promoted Mark Bierley to chief financial officer.

Tyson Foods Inc. said Monday that its president and chief executive, Dick Bond, will step down immediately and be replaced by a former CEO as the world's largest meat processor continues to weather a downturn. Bond, who had been CEO since 2006, will be replaced on an interim basis by former chairman and Chief Executive Leland Tollett.

New York Times Co. signed CBS Corp. as a front-page advertiser in its flagship newspaper starting today, in a long-term deal designed to help counter declining revenue. CBS became the first display advertiser on the front of The New York Times , with a color ad across the bottom of the page.

Several of the nation's largest airlines have joined in a lawsuit to block stronger federal rules on crew rest during the longest international flights. The airlines say that the Federal Aviation Administration bypassed usual rule-making procedures and denied them the right to comment before it notified American Airlines and Continental Airlines Inc. of the new rules in late October.

Meg Whitman , the former chief executive officer of eBay Inc., stepped down from the company's board as well as those of Procter & Gamble Co. and DreamWorks Animation SKG Inc. The departures were a signal that Whitman, a Republican, is seriously considering running for governor of California, the Wall Street Journal reported.

Israel's ground offensive in Gaza and a dispute between Ukraine and Russia over gas imports pushed oil prices above $48 a barrel Monday. Light, sweet crude for February delivery rose $2.47 cents to settle at $48.81 a barrel on the New York Mercantile Exchange.