Ukraine's National Coordination Center for Cybersecurity on September 20 banned the use of the Telegram messenger app for state officials, military personnel, and employees of key infrastructure, citing security issues.
https://www.currenttime.tv/a/ukrainskim-voennym-zapretili-ispolzovat-telegram/33127753.html
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the Dossier Center published an investigation into how Russian security officials may have leverage over the Telegram team, some of which are still in Russia. The publication cited one of its sources in the security forces, who said that Russian intelligence agencies are "confident that Telegram will not leak their data to the West."