Ukraine and Russia said their public emergency-warning apps were compromised late Sunday and early Monday, sending false alerts as a localized ceasefire in the Kherson region expired^1,2,4.

Ukraine's air force said the Air Alarm app had probably been subjected to hostile interference after users received baseless radiation and other warnings, and spokesman Yuriy Ignat confirmed a hack^1,4. Alerts around Kyiv included claims of radiation, a chemical threat, street fighting and a reference to Russia's Oreshnik missile; officials said there was no radiation threat^2,3. Ukraine's digital ministry temporarily disabled the app³. The Center for Strategic Communications SPRAVDI blamed Russia^1,2.

Hours later, Russia's emergencies ministry said a massive cyberattack let attackers send false information on an app meant to warn of drones and other threats, and that crews were working to fix it^1,4,5. Moscow did not immediately name a culprit^1,5. The BBC reported a Ukrainian espionage group claimed fake nuclear warnings were sent to users inside Russia³.

The hacks followed the end of a pause around occupied Oleshky that Ukraine said ran from Oct. 27 to Nov. 1 after Russia declined an extension^1,4,5. Ukrainian President Volodymyr Zelenskyy said Kyiv could stop striking Russian refineries if the United States provided Patriot missiles^4,5.