The National Academy of Sciences released a study November 14 finding that the U.S. electric grid is vulnerable to terrorist attacks that could cause more damage to the system than horrific natural disasters, blacking out large regions of the country for weeks or months at a time and costing billions of dollars. The Department of Homeland Security, which sponsored the report, classified the 2007 report, and the National Research Council was finally able to clear the report for public release after making a formal request for an updated security clearance.