Former Homeland Security head Tom Ridge unveils the color-coded system.  (Photo: CBS/AP ) In response to complaints that the broad terrorism alerts issued by the government in the months following the Sept. 11 attacks lacked useful guidance, the Homeland Security Advisory System (HSAS) was implemented on March 12, 2002. As threats are assessed, the warning level can be upgraded for the entire country or for specific regions and economic sectors. <<< Click the colors for more on each warning level. Credits:  CBS News, Dept. of Homeland Security