A hacked emergency alert app on Sunday night delivered a series of false alarms in Ukraine, including simulated nuclear strikes and chemical attacks, sparking initial unease but ultimately little panic among residents already accustomed to constant threats.

The app, which normally warns of Russian drone and missile attacks, began issuing increasingly severe alerts that quickly escalated to claims of impending nuclear strikes, chemical attacks, and street fighting. However, many Ukrainians questioned the authenticity of the messages.

Sofia Kochmar, a resident of Lviv, said she was initially concerned by the mention of "nuclear" but quickly doubted the warnings. "Then the notification mentioned 'street fighting in Kyiv,' and I thought, wait, no, that's impossible," she told BBC News.

The alerts, some of which were in Russian, included a link to a Telegram channel reportedly belonging to a hacker group. Within 15 minutes, Ukraine's Air Force stated that the alert app had been compromised and there was no radiation threat. However, it took over an hour to issue definitive "all clear" messages.

Anastasiia Romanytska, a Kyiv resident, said that although she did not have the app installed, 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," she said. "Still, somehow I immediately realised that it wasn't something serious."

Yevhen Baliutov, a cybersecurity expert at the Kyiv School of Economics, told the BBC that he believed the Ukrainian alert system was hacked by Russians. He noted that many Ukrainians had clicked a link included with the alerts, potentially exposing them to further disinformation or data breaches. "This is a war, so it's no surprise that Russia will try to hack, will try to send us fake news, will try to manipulate, and will use that for their propaganda," Baliutov said.

While both Russia and Ukraine are known to conduct cyberattacks, the informal language in the hoax alerts suggested the involvement of hacktivist groups, which may be aligned with Moscow or Kyiv but not formally directed by either government. Baliutov also suggested it was logical for Ukraine to respond with a cyber-attack on Russia's emergency alert system, given their similar capabilities.

Despite the scare, Kochmar observed that Ukrainians quickly turned to joking about the incident in their work group chats. "Everyone started messaging each other, discussing what was happening. And what I found fascinating was how quickly we turned the whole thing into a joke."

Baliutov cautioned that while the impact of this particular incident was limited, it highlighted a critical vulnerability in the alert system. "It's very dangerous for Ukraine and for our people," he stated. "When developing such applications, we need to consider security from the very beginning, without skipping essential security measures. When millions of people rely on a service, we cannot afford to take shortcuts with security."

Ukrainian authorities now face the challenge of maintaining public vigilance and reassuring citizens that the systems designed to protect them are robust and trustworthy, especially after four and a half years of war have already led to a degree of desensitization to constant air raid warnings.