Ukraine’s Major Mobile Operator Kyivstar Down During A Hacker Attack.

Ukrainians mobile phones subway Kyiv Ukraine 12 December 2023 Russia's invasion telecommunications Kyivstar large-scale failure users make calls receive calls internet services hacker attack operator's infrastructure local media STR NurPhoto cyber security network disruption telecommunications outage infrastructure attack cyber warfare emergency services communication breakdown network reliability cyber attack response mobile network IT infrastructure service restoration digital vulnerability national security war impact on telecom