Ukraine and Russia say their emergency alert apps have been hit by cyber-attacks – what we know in 100 words
In Ukraine, residents saw warnings including one for a "chemical threat" and another for "street fights"
Olena, who lives in Kyiv, tells BBC Radio 4's Today programme her "first thought" after seeing the alerts was"I'm prepared for blackouts, for a cut in central heating and water supply, but not for a nuclear attack"
The air force went on to clarify there was no imminent threat of nuclear war, blaming Russian interference, writes our correspondent in Kyiv
Later, Russia itself said a "massive cyber-attack" had affected its app, with the emergencies ministry saying specialists were working to restore it
If this is confirmed as a tit-for-tat scenario, it implies that whoever struck second had the power to carry out the hack but chose to hold off until its own system was hit, writes our cyber correspondent
Meanwhile, strikes were reported overnight in both countries, with four people injured in the Ukrainian city of Odesa and Russia saying drone strikes hit an industrial complex east of Moscow
Edited by Charlotte Hadfield
Ukrainian MP Oleksandr Merezhko says he can neither confirm nor deny if Ukraine was behind a reported cyber attack on Russia, which occurred shortly after a cyber attack on Ukraine.
Merezhko says Ukraine believes Russia was likely behind the cyber attack on Ukraine's emergency warning system, as the warnings were issued in Russian, as opposed to Ukrainian.
However, he says there is "no official confirmation, as of yet at least" that Ukraine was responsible for a cyber-attack on Russia's emergency app.
"In such cases we don't confirm or don't deny," adds Merezhko, who is also head of the foreign affairs committee in the Ukrainian Parliament.
On the reaction to the fake alerts, he says Ukrainians have "unfortunately" become used to constant alerts, to the point where people "tend to treat all kind of information with a certain scepticism".
"Luckily in this case there was swift action from the air force, saying that it was a fake alert," he adds.
Joe Tidy
Cyber correspondent
It is very strange to see both sides being hit in near simultaneous cyber attacks on two similar but entirely separate alert systems.
I reached out to a contact in the Ukrainian hacktivist community who said that it suggests that Ukraine hacked Russia’s alert system as part of a retaliation.
“Most likely this was a retaliatory hack” the hacker said.
The contact says that hacking alert systems is a tactic that, until now, had "not been used due to moral and ethical considerations".
Social media reports show that the Ukrainian app Trivoha was hacked first and then Russia’s equivalent was hit shortly after.
On a popular Ukrainian Telegram group about air raids, the messages show discussions about the hack of Trivoha followed by screenshots of Russia’s alert system showing the hack message to Russians.
The poster on the group of 20,000 celebrated the apparent strike back saying “haha, quickly”.
It is not clear, though, which alert system was hit first.
If this is confirmed as a tit-for-tat scenario, it implies that whoever struck second had the power to carry out the hack but chose to hold off until its own system was hit.
There has been no official response though and no groups have yet claimed responsibility. 
Katie Williams
Live reporter
Ukraine and Russia both say their emergency warning apps have been hit by cyber-attacks overnight. Here's the latest:
In Ukraine
Ukraine appears to have been hit first, with false red-level air raid alerts starting at approximately 22:47 local time (20:47 GMT) on Sunday.
Kyiv was hit by additional false warnings for radiation, chemical attacks and street fighting – here's a timeline.
Ukrainian politician Oleksander Merezhko says the fact a message was in Russian "immediately aroused suspicions", calling hacking "part of cyber war".
In Russia
A few hours later, Russia said its app had been hacked in a "massive cyber-attack" with hackers "able to distribute false information to the public".
The false alert warned app users there was a "risk of getting lively", and said nuclear warheads had been launched "at all regions of Russia".
Russia's emergency ministry called the app "an additional, ancillary news service" and says its public alert system is "operating as normal".
It is unclear if the two incidents are connected, our correspondent in Kyiv reports.
We can now bring you some reaction to the apparent cyber-attacks from a resident in Kyiv, who tells the BBC of her shock after receiving false emergency alerts warning of radiation and the threat of nuclear attack.
"The first thought was 'Oh my god, I'm not prepared for this'," Olena tells Radio 4's Today programme.
"I'm prepared for blackouts, for a cut in central heating and water supply, but not for nuclear attack," she adds.
Olena says her husband then received alerts for "street fighting attacks in Kyiv" and another alert, written in Russian.
"After that I understood that somebody had attacked the app, because all notifications we get in Ukrainian."
Police officers from the evacuation unit pictured in Ukraine's Komyshuvakha, in the Zaporizhzhia region, on October 19
Four people have been injured in air strikes on Ukraine's Zaporizhzhia region, according to co-chair of the regional defence council Ivan Fedorov.
No immediate update is given on their condition.
Sharing the update on Telegram, Fedorov adds that there were also 43 reports of damage to homes, vehicles, and infrastructure in the region.
Separately, Ukraine's armed forces says hits from air strikes were recorded at 26 locations across the country overnight, with debris falling at another nine locations.
It says 154 Russian drones were intercepted by air defences.
While we wait for further information on the apparent cyber attacks in Russia and Ukraine, here's the latest on the strikes that were reported overnight.
In a statement on Telegram, Russia's Ministry of Defence says it struck a Ukrainian military cargo vessel at sea 58km south of Odesa overnight.
It says the vessel was "delivering cargo intended for the Ukrainian Armed Forces".
Another strike hit a storage site for Ukrainian missile launch systems in the Odesa village of Tuzly, it says.
Meanwhile, a Telegram channel for the city of Odesa says four people were injured in strikes in Odesa overnight. "All received prompt medical assistance," the update says.
It adds that two private homes, a garage and city infrastructure also sustained "significant damage".
The false alerts started at approximately 22:47 (20:47 GMT) on Sunday, with red-level air raids apparently issued nationwide, in Ukrainian.
Additional warnings were issued in Kyiv, with the first reading: "Radiation threat. Radiation threat declared in Kyiv."
The next message, written in Russian, came at 22:48, which read: "Hi! There will be a nuclear alert across Ukraine. Don't worry, it's Oreshnik flying". Oreshnik is the name of a Russian intermediate-range ballistic missile capable of carrying nuclear or conventional warheads.
A third alert, at 22:49, again in Ukrainian, said "Chemical threat. There is a threat of a chemical attack on Kyiv. Don't go outside."
At 22:49, a fourth alert stated there was a "street fighting threat. Street fighting is taking place in Kyiv. Don't go outside."
At 23:53 a series of all clear messages were then delivered to users' phones, which were connected to each of the previous Kyiv alerts, individually declaring each threat clear.
We don't know much about the alerts sent out in Russia. But as we reported earlier, a Ukrainian espionage group claimed fake warnings of nuclear strikes inside Russia had been sent to users.
Dan Johnson
Ukraine correspondent, reporting from Kyiv
Ukraine’s air raid alert app usually warns of incoming Russian drones or missiles.
Last night it issued alerts of a radiological threat, a chemical attack and street fighting here in Kyiv.
The warnings were followed by all clear messages just over an hour later.
The air force issued a statement saying the app had been hacked and reassured citizens there was no imminent threat of nuclear war, blaming Russian interference.
Hours later, Russia’s emergencies ministry claimed it had also suffered a cyber attack and said people were receiving emails containing fake information.
It’s not clear if the two incidents are connected.
Oleksander Merezhko, chair of the Ukrainian parliament's foreign affairs committee, has told the BBC the attack did not cause panic or extreme reactions.
Merezhko says Ukrainians, especially in Kyiv, are used to "practically non-stop alerts".
"Secondly, this message was in Russian language which immediately aroused suspicions," he says.
"It's a very unpleasant fact but it is part of cyber war and people in Ukraine understand that. It is possible and we are quite prepared for such possibilities," adds Merezhko, a member of President Volodymyr Zelensky's Servant of the People party,
Russia and Ukraine both say their emergency alert systems have been hit by cyber-attacks. Here's what we know so far:
The BBC's Newsday programme has just spoken to Herbert Lin, a senior research scholar for cyber policy and security at Stanford University, who describes the hacking of Ukraine's air strike alert system as "concerning".
“I think it’s the first time it’s happened to an official Ukrainian information app, but I suspect it won’t be the last,” says Lin, who previously served on former US President Barack Obama’s Commission on Enhancing National Cybersecurity.
“We don’t know how they did it yet… Maybe in the future they’ll be able to do it more but we just don’t know yet.”
Russia and Ukraine have also exchanged strikes targeting each other's energy infrastructure.
Russia said drone strikes hit an "industrial enterprise" east of Moscow overnight on Saturday, which Ukrainian media identified as the Kstovo oil refinery.
The governor of Russia's Nizhny Novgorod region – home to the Kstovo plant – described a "massive" drone attack during the night and morning.
Gleb Nikitin said significant damage was sustained and warned of power outages and reduced hot water supplies. He said one woman was injured as a result of falling drone debris.
Ukrainian forces have repeatedly attacked Russian oil and gas sites in retaliation for Russian attacks on Ukrainian energy infrastructure.
Ukrainian President Volodymyr Zelensky said Russia had struck energy infrastructure in four regions overnight on Saturday, leaving hundreds of thousands of homes without power. A Reuters report quoted him as saying the intensity of these strikes were "very high".
Some connections were restored on Sunday.
Aftermath of a Russian drone strike in Kramatorsk, Ukraine on 1 November
The fake alert sent to Russia's emergency app had warned users that "nuclear warheads mounted on P1-Suns [a Ukrainian attack drone] had been launched at all regions of Russia".
The alert, which opened with a message telling residents there was a "risk of getting lively" also told them to "stock up urgently on food for three weeks and hide".
Emergency alert apps in Ukraine and Russia have been hacked, according to reports.
The Ukraine government's Center for Strategic Communications has blamed Russia for the hack in a post on its X account, saying one of the alerts was a "message in Russian about Oreshnik".
A few hours later, Moscow also said that its emergency alert app had been hit by a "massive cyber-attack" – but did not immediately say who might be behind it.
Ukraine's Centre for Strategic Communications has blamed Russia for the hack in a post on its X account.
It posted a picture showing some of the alerts that had showed up on Ukraine's air raid warning app and asked residents to "disregard" any "strange messages" they might see in the app.
The Russian emergencies ministry says its public alert system is "operating as normal", stressing that citizens are informed of alerts through multiple channels including sirens and loudspeakers, text messages, and TV and radio broadcasts, and that the app is "only an additional, ancillary news service".
"The hacking of the mobile app has not had, and cannot have, any impact on the operation of the public alert system," it said on its Telegram channel.
It said specialists were working to restore normal operation of the mobile app but the situation was "under control".
Abdujalil Abdurasulov
Ukraine reporter
The false warnings were sent out just minutes before the end of a ceasefire in the Ukrainian frontline city of Oleshky, which has been under Russian occupation since 2022.
The rare six-day ceasefire had allowed hundreds to evacuate from Oleshky, in a deal that was brokered with the help of US First Lady Melania Trump and Pope Leo XIV.
It was the longest a ceasefire has held since the start of Russia’s full-scale invasion.
But the fighting is likely to resume in Oleshky as both sides have accused each other of using this period to strengthen their frontline forces. And yet, the humanitarian mission has sparked some optimism.
Officials in Kyiv say that it can lead to "systemic solutions" and "pave the way for further steps in the peace process".
Yana Lantratova, who coordinated the Oleshky operation from the Russian side, says that both countries have agreed to carry out "regular humanitarian missions".
But as Vladimir Putin’s spokesperson puts it, the Kremlin sees such operations as separate from the peace process.
The country's air force quickly responded after alarming false alerts on its air raid alert app for a short time said the capital Kyiv was subject to a radiation threat.
"The Air Alarm application has probably been subjected to hostile interference. There is no radiation threat! Stay calm and follow our updates on our channel," the air force said on Telegram.
The Ukrainian Central Intelligence Agency says there was a failure in the Air Alert app, and urges people to use other sources of information to clarify the situation on the threat of air strikes.
The app is supported by the Ministry of Digital Transformation of Ukraine, and informs users instantly about the beginning and end of defence alerts.
Ukraine and Russia are reporting cyber-attacks on their emergency alert apps, with fake warnings sent to users around the countries.
Ukraine was first to report problems, and for a short time the capital Kyiv was subject to a radiation threat, the Ukrainian Air Force has said.
A few hours later Russian authorities said its app was hacked, with a Ukrainian espionage group reportedly sending fake warnings of nuclear strikes inside Russia.
Stay with us as we bring you the latest developments.
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