The attack in Moscow shattered the illusion of security that Putin sells to the Russian public - voila! news. The massacre, which was carried out in a concert hall in the Moscow region, not far from the Kremlin, happened a few days after Putin won elections known in advance and despite American warnings.
Despite accepting the responsibility of ISIS, Russia was quick to link the attack to Ukraine in order to cover up the embarrassment and possibly justify the escalation of the war. As the four terrorists, and Ukraine on a daily basis, proved, in Putin's time it is very penetrating from a security point of view.