Kyivstar, Ukraine's largest mobile and Internet operator, which was targeted by a massive cyberattack this week, says it has restored Internet connectivity to 93 percent of its home subscribers after managing to bring back mobile phone services late on December 13.
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"In some settlements, we're still facing some short-term difficulties, but our specialists are in the process of eliminating them," Kyivstar said in a statement on December 14, adding that the company, which has some 24.3 million cell phone subscribers and more than 1.1 million home Internet users, continues "to cooperate with Ukraine's Security Service (SBU) and other relevant state authorities to establish all the circumstances of the attack."
The company promised to compensate its clients for the duration of the outage.
The hack that brought down Kyivstar's cellular and Internet signal caused serious disturbances in communications across Ukraine and left millions without service in the war-torn country.
Ukraine’s Security Service (SBU) has said that its cyberspecialists are working to repair the network in cooperation with Kyivstar and other governmental agencies. The SBU also said it had opened a criminal case over the hack.
"One of the versions currently being investigated by the SBU investigators is that the special services of the Russian Federation may be behind this hacker attack," the SBU told RFE/RL.
A group of activist hackers called Solntsepyok said on Telegram that it carried out the cyberattack.
Ukraine's State Service of Special Communications and Information Protectorate (SSSCIP) said in a statement that responsibility for the attack has been claimed by a Russian group whose activities are associated with the main directorate of Russia's GRU military intelligence agency.
"This once again confirms Russia's use of cyberspace as one of the domains of the war against Ukraine," it said, without naming the group that has claimed responsibility.
Earlier this year, the SSSCIP identified Solntsepyok as a front for a Russian hacking group dubbed Sandworm, which has been previously linked to the GRU.
Sandworm has been tracked by cybersecurity researchers as having been responsible for cyberattacks against Ukraine’s energy sector.