Russian hackers were inside Ukrainian telecoms giant Kyivstar’s system from at least May last year in a cyberattack that should serve as a “big warning” to the West, Ukraine’s cyber spy chief told Reuters.The hack, one of the most dramatic since Russia’s full-scale invasion nearly two years ago, knocked outservices provided by Ukraine’s biggest telecoms operator for some 24 million users for days from Dec. 12.In an interview, Illia Vitiuk, cyber chief for the Security Service of Ukraine (SBU), disclosed exclusive details about the hack, which he said caused “disastrous” destruction and aimed to land a psychological blow and gather intelligence.During its investigation, the SBU found the hackers probably attempted to penetrate Kyivstar in March or earlier, he said in a Zoom interview on Dec. 27.The SBU assessed the hackers would have been able to steal personal information, understand the locations of phones, intercept SMS messages and perhaps steal Telegram accounts with the level of access they gained, Vitiuk said.A Kyivstar spokesperson said the company was working closely with the SBU to investigate the attack and would take all necessary steps to eliminate future risks, adding: “No facts of leakage of personal and subscriber data have been revealed.”Vitiuk said the attack was not accompanied by a major missile and drone strike at a time when people were having communication difficulties, limiting its impact while also relinquishing a powerful intelligence-gathering tool.Why the hackers chose Dec. 12 was unclear, he said, adding: “Maybe some colonel wanted to become a general.”‘