The Ukrainian government has accused Russia of being behind Friday's cyber attack on dozens of official websites.
About 70 government websites were temporarily shut down, in the largest such attack in Ukraine in four years.
Before the sites went offline, a message appeared warning Ukrainians to "prepare for the worst." Access to most sites was restored within a few hours.
The US and NATO condemned the attack and offered support to Ukraine. Russia has not commented on the hacking.
Experts at the Ukrainian Ministry of Information published a timeline of how the news of the attack spread, noting that Russian media reported it to the Ukrainian media.
They claimed the attacks were in response to what they called Russia's failure in its recent talks with NATO over Ukraine.
Ukraine has come under great pressure from its neighbor, with a gathering of about 100,000 Russian troops near its borders, reports rtv21.tv
Ukraine's SBU security service says it "neutralized" 1200 cyber attacks or incidents in just nine months last year.
NATO said it would soon sign an agreement with Ukraine on enhanced cyber cooperation, which would give it access to the alliance's malware exchange platform.
The White House says it will provide Ukraine with all the support it needs to recover from the attack.
At the start of Friday's attack, a message was posted on hacked websites in three languages, Ukrainian, Russian and Polish.
“Ukrainians! All your personal information is uploaded to the public internet. "This is about your past, present and future," the message said.
The message in Polish contained serious errors and did not appear to have been written by a native speaker, according to a statement issued by the Polish government.21Media