New York  - US stocks tumbled Monday amid concerns over the fate of the struggling car industry, which will be given a last chance to restructure operations or lose government support.

President Barack Obama said that General Motors Corp and Chrysler LLC had so far failed to prove that they can survive. He called for a series of changes in the two companies' outdated business models and forced out long-time GM chief executive Rick Wagoner.

Washington  - President Barack Obama on Monday approved a sweeping expansion of government land protections, safeguarding about 800,000 new hectares of parks, rivers, forests and mountains across the United States.

The legislation, which is a collection of about 150 smaller bills that had been in the works for years, was approved earlier this month with broad bipartisan support by both chambers of Congress.

The bill designates new wilderness areas across nine US states, including mountains in California, Virginia and Colorado, protecting those regions from any kind of commercial development.

San Francisco - Researchers have discovered the first easy way to detect the presence of the Conficker computer worm on networked computers, just days before the worm is scheduled to morph into a new form that could seriously compromise millions of computers, PC magazine reported Monday.

San Francisco - A new study has found that action video games can improve players' eyesight, researchers said Monday.

The study, which was published in the journal Nature Neuroscience, found that the visual processes needed to play games like Call of Duty 2 improved players' contrast sensitivity. Contrast sensitivity allows people to notice different shades and is particularly important for such tasks as driving at night and discerning patterns and facial expressions.

Washington  - Struggling US carmaker Chrysler LLC and Italian maker Fiat Motor SA said Monday they had reached a deal in principle on a new partnership, less than two hours after the US government said the merger was the only way for Chrysler to keep its emergency loans.

Chrysler chief executive Bob Nardelli, announcing the agreement, said the alliance would help the US carmaker preserve jobs and build more fuel-efficient cars.

"Chrysler has consistently said that the alliance with Fiat enhances its business model (and) expands its global competitiveness," Nardelli said in his statement.

Washington - The United States on Monday welcomed an Afghan Supreme Court ruling extending President Hamid Karzai's term until an election in August.

The court ruled Sunday that Karzai should stay in power after his term ends May 22, until the elections are held.

"The United States strongly supports and welcomes this ruling," said State Department spokesman Gordon Duguid. "We believe that the continuity of government in this critical period before elections is vital and contributes to creating stability."