Ukraine's largest mobile phone operator, Kyivstar, is down after being targeted by a massive hacker attack on December 12 that brought down its cellular and Internet signal, causing serious disturbances in communications across the country and leaving millions without service in the war-torn country.
"This morning we were the target of a powerful hacker attack. It caused a technical failure that made mobile communication and Internet access temporarily unavailable," Kyivstar said in a statement, while its chief executive officer, Oleksandr Komarov, told Ukrainian television that the network had to be shut off in order to ban what he called "enemy access."
The cyberattack reportedly left more than 24 million subscribers without service. Card payments were disturbed throughout Ukraine, as Kyivstar's system is critical for card payments in most commercial outlets.
"(The attack) significantly damaged the (IT) infrastructure and limited access. We could not counter it at the virtual level, so we shut down Kyivstar physically to limit the enemy's access," Komarov told state TV.
Law enforcement agencies including Ukraine's Security Service (SBU) were looking into the incident, Komarov said, adding, "This is a war, waged not only on the battlefield but also in virtual space and, unfortunately, we are targeted in this war."
The SBU's press service confirmed to RFE/RL that it launched an investigation into the cyberattack, saying the probe was looking into "unsanctioned interference into the activities of social networks, the creation of malware, encroachment of the territorial integrity of Ukraine, high treason, sabotage, the conducting of an aggressive war, the violation of the law of war, and taking part in a criminal group's activities."
Russia has been repeatedly attempting to use cyberattacks against Ukraine since the start of its unprovoked full-scale invasion in February last year, while Kyiv has done likewise.
The Main Directorate of Ukraine's Military Intelligence (HUR) said in a statement on December 12 that it conducted a "successful" cyberattack on Russia's Federal Tax Service.
Kyivstar said its clients' personal data had not been compromised while Deputy Prime Minister Oleksandr Kubrakov told the media that Kyivstar would resume operations within four to five hours.
However, Kyivstar was still down in the early afternoon local time, and authorities in Sumy said the air-raid alert system in the northeastern city "was temporarily out of order," AFP reported.
In the western city of Lviv, Ukraine's fifth-largest, street lighting controlled through Kyivstar's network remained on through the morning but had to be managed manually.
Interior Minister Ihor Klymenko said mobile numbers for emergency services continue to operate normally.
Meanwhile, Monobank, one of Ukraine's largest online banks, said it had repelled a massive distributed denial-of-service (DDoS) attack.
"Repelled. Mono is impenetrable," Mono's co-founder Oleh Horokhovskiy said on Telegram.
A DDoS attack is one in which hackers flood a website with requests for information, making it unavailable to legitimate users.
