From ABC News:

Terrorism experts today warned that Monday’s bus bombing in southern Russia could be the opening salvo in a new series of plots from a desperate extremist group that may target civilians up to and during the 2014 Olympics in Russia, despite assurances from Olympic organizers. Monday’s bombing in Volgograd in southern Russia was carried out by a 30-year-old woman from Dagestan, authorities said, who was reportedly married to an explosives expert in the Islamic insurgency in the North Caucasus.