ABC News: Suspicious packages from Yemen intercepted in Dubai and England tested positive for explosives, according to President Obama, addressing the nation Friday afternoon about what he now calls "a credible terror threat." The president said the devices were possibly targeting Jewish community groups in the Chicago area. He vowed to enhance screening of cargo planes in the U.S. An intelligence report that al Qaeda in Yemen may have shipped an explosive device to Chicago led to an international search of cargo planes carrying packages to the United States from Yemen today.