“Such attacks are usually perpetrated by countries,” he said. “Such attacks need infrastructure.”
Moscow denied responsibility for the DDoS attack. “We know nothing about it, but we are not surprised that Ukraine is continuing to blame Russia for everything,” Kremlin spokesman Dmitri S. Peskov told journalists. “Russia has nothing to do with any DDoS attacks.”
Mr. Vityuk said that the attack bore similarities to a mid January attack in which hackers brought down dozens of Ukrainian government websites, including Ukraine’s Ministry of Foreign Affairs.
At the time, a message on the Ministry of Foreign Affairs warned: “Ukrainians! All your personal data was uploaded to the internet. All data on the computer is being destroyed. All information about you became public. Be afraid and expect the worst.”
On Tuesday, clients of the state-owned PrivatBank and Oschadbank began to complain about difficulties using teller machines and mobile phone applications. The banks confirmed the attack, but said the funds in users’ accounts had not been affected, though users said they had been temporarily unable to withdraw money or use their credit cards. Some clients of the banks were worried, as their bank balances appeared drained. By Tuesday evening that most services had been restored.
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Pavlo Kukhta, an adviser to Ukraine’s energy minister, said in an interview that the hackers were possibly preparing for a larger attack, which could target the country’s “vulnerable” power grid.
“The goal is quite simple: to sow panic, show what they are capable of, test the systems and see if they are vulnerable,” he said. “They are poking around and looking for weaknesses.”
As of Wednesday evening, the DDoS attack, which began at 3 p.m. Kyiv time on Tuesday, had been going on for more than 24 hours, Ukraine’s Defense Ministry said. Ukrainian cybersecurity officials “have managed to significantly reduce the level of harmful traffic,” said Victor Zhora of the Center for Strategic Communications and Information Security, a government agency established to counter Russian disinformation.