In a series of statements posted to Twitter, the company said the data-wiping program had been "installed on hundreds of machines in the country," an attack it said had likely been in the works for the past couple of months.
Vikram Thakur of cybersecurity firm Symantec, which is also looking into the attacks, told Reuters that infections had spread widely.
"We see activity across Ukraine and Latvia," Thakur said. A Symantec spokesperson later added Lithuania.
Who is responsible for the wiper is unclear, although suspicion immediately fell on Russia, which has repeatedly been accused of launching data-scrambling hacks against Ukraine and other countries. Russia has denied the allegations.
Ukraine has already been repeatedly hit by hackers in the past few weeks as Russia has massed troops around its borders. Fears of a full-scale invasion rose after Moscow this week ordered troops to two separatist regions in eastern Ukraine.
Cybersecurity experts are racing to pick apart the malicious program, a copy of which was uploaded to the Alphabet-owned crowdsourced cybersecurity site VirusTotal, to see what its capabilities were.
Researchers found that the wiping software appeared to have been digitally signed with a certificate issued to an obscure Cypriot company called Hermetica Digital Ltd.
Because operating systems use code-signing as an initial check on software, such a certificate might have been designed to help the rogue program dodge anti-virus protections. Getting such a certificate under false pretences - or stealing it - isn't impossible, but it's generally the sign of a "sophisticated and targeted" operator, said Brian Kime, a vice president at US cybersecurity firm ZeroFox.
Contact details for Hermetica - which was set up in the Cypriot capital, Nicosia, almost a year ago, were not immediately available. The company did not appear to have a website.
Earlier on Wednesday the websites of Ukraine's government, foreign ministry and state security service were down in what the government said was the start of another denial of service (DDoS) attack.
In a statement, Ukraine's data protection watchdog said that hacks were increasing.
"Phishing attacks on public authorities and critical infrastructure, the spread of malicious software, as well as attempts to penetrate private and public sector networks and further destructive actions have intensified," it said in an email.
Last week, the online networks of Ukraine's defence ministry and two banks were overwhelmed in a separate intrusion. The US company Netscout Systems Inc later said the impact had been modest.
Ukraine has suffered a drumbeat of digital assaults that Kyiv and others have blamed on Russia since 2014 when Moscow annexed the Crimean peninsula and backed a separatist rebellion in eastern Ukraine.
The Kremlin has denied any involvement.
