Reported by BBC World
Watch: Ukraine and Russia say emergency apps hit by cyber-attack
Ukrainians have grown weary of the relentless alerts blaring from their phones and echoing through their streets, day and night, warning of Russian drones and missiles.
On Sunday night, the system delivered something to make them sit up and take note – a succession of more extreme threats that quickly escalated to impending nuclear strikes, chemical attacks and combat on the streets.
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But many in the country did not take them seriously and doubted the veracity of the messages.
Sofia Kochmar, 34, a mother-of-one living in the western city of Lviv, said she was initially concerned but quickly questioned the authenticity of the alerts.
"The first thing I saw was the word 'nuclear' and that made me pretty nervous and scared. So my first thought was that something nuclear was actually flying toward us."
"But then the notification mentioned 'street fighting in Kyiv', and I thought, wait, no, that's impossible."
The alerts included some messages written in Russian, and one included a link to a Telegram channel apparently owned by a hacker group.
Within 15 minutes, Ukraine's Air Force issued a statement saying the alert app had been compromised and clarifying there was no radiation threat. But it took more than an hour to issue "all clear" messages.
Anastasiia Romanytska, a 29-year-old ballerina living in Kyiv, said she does not have the alert app installed but friends forwarded her the warnings.
"My first reaction was, 'Is this some kind of joke?' But then my body reacted as if I was under stress. My heart started racing, and my stomach tightened up."
"Still, somehow I immediately realised that it wasn't something serious. Or maybe I just really wanted to believe that."
There are a number of apps delivering phone notifications of air raid warnings, with maps showing areas under threat, all using the same data as the official government-backed app.
Ukrainians have different apps with official data to warn them about air raid warnings
Yevhen Baliutov, a cybersecurity expert at Kyiv School of Economics, told the BBC it was clear to…