The cyber attack on Ukraine's largest mobile operator Kyivstar is likely one of the most destructive cyber attacks on Ukrainian networks since the start of the full-scale Russian invasion, as Ukrainian government resources and emergency services were affected, according to a report from the UK Defense Intelligence on the social network X (formerly Twitter).

"On December 12, Kyivstar, Ukraine's largest mobile network operator, suffered a cyber attack. Effects continued for at least 48 hours, impacting the company's mobile and data services. Kyivstar supplies over half of Ukraine' population with mobile and home Internet services. The cyber attack reportedly left users without mobile signal or the ability to use the Internet. Kyivstar reported that no personal data was compromised during the attack," the report reads.

"The cyber attack also reportedly disrupted air raid sirens, some banks, ATMs, and point-of-sale terminals. At the same time, the Ukrainian bank Monobank was targeted with a Disrupted Denial of Service (DDoS) attack, disrupting access to the bank's website," it says.

"With Ukraine's government resources and emergency services affected, this incident is likely one of the highest-impact disruptive cyber attacks on Ukrainian networks since the start of Russia's full-scale invasion," according to the report.