The US on Friday confirmed that a recent series of cyberattacks against the Ukraine government was carried out by Russia.

The confirmation came from the White House on Friday, with Deputy National Security Advisor for Cyber and Emerging Technology Anne Neuberger telling the press, “We believe that the Russian government is responsible for widescale cyber-attacks on Ukrainian banks this week.”

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“We have technical information that links the Russian Main Intelligence Directorate, or GRU, as known GRU infrastructure was seen transmitting high volumes of communication to Ukraine based IP addresses and domains,” Neuberger further said.

Days earlier, DDoS attacks had brought down the websites of several Ukrainian banks and government institutions, including those of the Defense Ministry, the Foreign Ministry, and the Culture Ministry, as well as those of major banks such as Privatbank and Sberbank.

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However, Neuberger did not confirm whether the attack against government institutions that took place around the same time were also the work of Russian hackers.

The attribution of responsibility for the cyberattack against Ukrainian banks was unusually fast for the US, which typically takes longer periods of time to issue a confirmation.

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Neuberger also said that Russia benefitted from such delays, telling reports in the White House briefing room, “Russia likes to move in the shadows and counts on a long process of attribution so it can continue its malicious behavior against Ukraine in cyberspace, including pre-positioning for its potential invasion.”

She went on to say that the US government had shared the “underlying intelligence” behind the attribution to Ukraine and its European allies, and warned that the cyberattacks could be a precursor to further cyberattacks to cripple Ukraine ahead of a full-scale Russian invasion.

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“While of limited impact, this recent spate of cyberattacks in Ukraine are consistent with what a Russian effort could look like in laying the groundwork for more disruptive cyberattacks accompanying a potential further invasion of Ukraine sovereign territory,” she said, highlighting the disruptive threat posed by Russian hackers.

Neuberger further told reporters that the US government had been preparing for the possibility of Russian aggression since November and had “intensified” its support for the Ukrainian government in light of recent developments.