Ukraine’s cyber spy chief revealed that Russian hackers had infiltrated the country’s largest telecoms operator for several months, in one of the most dramatic cyberattacks related to the ongoing conflict. The hackers, who are believed to be linked to Russia’s military intelligence agency, the GRU, gained access to the network of Ukrtelecom, which serves about 24 million customers, in May last year. They were able to collect personal data, track phone locations, intercept messages and potentially compromise Telegram accounts, according to the head of Ukraine’s Cybersecurity and Information Protection Service, Serhiy Demedyuk. The hack was discovered in December, when the hackers launched a massive denial-of-service attack that disrupted Ukrtelecom’s services for days. Demedyuk said the attack was part of Russia’s hybrid warfare strategy, which combines conventional, cyber and information operations to undermine Ukraine’s sovereignty and security. He also warned that the hackers could still have access to some parts of Ukrtelecom’s network, and that other critical infrastructure sectors, such as energy and banking, could be targeted as well.