As part of the investigation of a suicide bombing attack, Russian authorities requested providers to disable security mechanisms in their mobile networks, to allow eavesdropping on all calls.

Mobile users were notified of the reduced level of security in their calls by an icon on mobile phones, showing either an exclamation mark, or an unlocked padlock.

The decision to shut down encryption follows the double suicide bombings that killed 14 people at the Krylya rock festival Saturday. A cellphone was found on one of the female suicide bombers, and the FSB is examining its SIM card for clues as to whether the bombers coordinated the attack with accomplices, according to local media reports.

According to Russian authorities this procedure is covered by law, and was used before a during the Dubrovka theater crisis in October, when a group of 41 Chechen rebels took more than 800 people hostage.