The turmoil comes as tensions rise with Russia, with NATO and the European Union promising to help Kiev face more attacks.
A massive cyber attack left Ukrainian government websites temporarily unavailable on Friday, officials said.
While it is not clear who was behind the cyber attack, the turmoil came amid heightened tensions with Russia and after talks between Moscow and the West failed to make any significant progress this week.
It is too early to know who was behind the attack, “but there is a long record of Russian cyber-attacks against Ukraine in the past,” Ukrainian Foreign Ministry spokesman Oleg Nikolenko told the Associated Press.
Moscow has previously denied involvement in cyber attacks against Ukraine.
The websites of the country’s Cabinet, seven ministries, the Treasury, the National Emergency Service and the State Services website, where Ukraine’s electronic passports and vaccination certificates are stored, were temporarily unavailable on Friday as a result of the hack.
The sites contained a message in Ukrainian, Russian and Polish, stating that the personal data of Ukrainians had been leaked into the public domain.
“Be afraid and expect the worst. This is for your past, present and future,” the letter was partially read.
The Ukrainian State Service for Special Communications and Information Protection said that no personal data had been leaked. Most of the affected websites were restored later on Friday and no critical infrastructure was affected.
The timing of the distortion and provocative message could be important, said Oleh Derevianko, a leading expert in the private sector and founder of cybersecurity firm ISSP.
It could be “part of a planned hybrid attack or a longer-range and more complex cyber operation that is underway but has not peaked,” Derevianko said, the main question being Whether this is a single act of hacking or part of a larger state-backed operation.
Tensions between Ukraine and Russia have risen in recent months after Moscow massed an estimated 100,000 troops near the Ukrainian border, raising fears of an invasion.
Moscow has said it has no plans to attack and rejects Washington’s request to withdraw its forces, saying it has the right to deploy them where necessary.
The Kremlin has demanded security guarantees from the West that NATO rejects its membership in Ukraine and other former Soviet states and ends the alliance’s military deployment in Central and Eastern Europe. Washington and its allies refused to make such pledges, but said they were ready for talks.
NATO Secretary General Jens Stoltenberg said Friday that in the coming days, “NATO and Ukraine will sign an agreement on strengthening cyber cooperation, including Ukrainian access to NATO’s malware information sharing platform.”
The European Union’s foreign policy chief, Josep Borrell, said Friday that the bloc is ready to mobilize resources to improve Ukraine’s ability to counter cyberattacks.
“Unfortunately, we expected this to happen,” he said.
Asked who could be behind the attack, Borrell said: “I can’t point to anyone because I don’t have proof, but one can imagine.”
Russia has a long history of launching aggressive cyber operations against Ukraine, including hacking its voting system ahead of the 2014 national elections and assaulting the country’s power grid in 2015 and 2016. The NotPetya virus targeted Ukrainian companies and caused more than 10 billion damage dollars worldwide.
In a separate development, Russia said on Friday it had dismantled the prominent hacking group REvil, which carried out a major attack last year on IT software company Kaseya, at Washington’s behest.
Cyber security was one of the main issues on the agenda of the summit meeting between Russian President Vladimir Putin and US President Joe Biden last June.
The Russian Federal Security Service (FSB) said in a statement that it had “repressed the illegal activities” of members of the group during raids at 25 addresses and swept 14 people.
The inspections were carried out following “an appeal by the relevant US authorities”.