Never before in American history had so many people received a text message at the exact same time. It was bearing grave, unthinkable, catastrophic news – and it wasn't even true.

A little over a year ago, this is what more than a million people in Hawaii saw on their phones, television screens, and flashing on billboards across the state: BALLISTIC MISSILE THREAT INBOUND TO HAWAII. SEEK IMMEDIATE SHELTER. THIS IS NOT A DRILL.

As we know now, it really wasn't a drill. But nor was this terrifying prospect actually real.

The perceived ballistic missile threat broadcast all over Hawaii on 13 January 2018 was a textbook false alarm: the result of inadequate technical safeguards and a clumsy mistake made by somebody who simply did the wrong thing at work one day.

In the fallout, that worker was first reassigned, then subsequently let go for performance issues, while other officials resigned from their positions.

But at 8:07 am local time on 13 January, nobody in Hawaii knew any of that.

All they knew was what they'd been told by the authorities in the emergency alert appearing on basically every screen in the state: that a ballistic, possibly nuclear missile had been launched at them, and they needed to find cover right now if they wanted to survive the imminent explosion.

Alerts appearing on TV went into even further detail about the emergency than the SMS warnings:

"The US Pacific Command has detected a missile threat to Hawaii. A missile may impact on land or sea within minutes. THIS IS NOT A DRILL. If you are indoors, stay indoors. If you are outdoors, seek immediate shelter in a building. Remain indoors well away from windows. If you are driving, pull safely to the side of the road and seek shelter in a building or lay on the floor. We will announce when the threat has ended. THIS IS NOT A DRILL. Take immediate action measures."

Predictably, mass panic ensued.

Parents shoved their children down storm drains. Family members desperately called and texted loved ones to say goodbye. People sat together in bath tubs. One man had a heart attack while standing on the beach, waiting for the end to come.

People also tweeted, a lot, and in a bid to better understand how the public reacts to emergency predicaments like Hawaii's 2018 false missile alert, researchers at the CDC analysed over 14,000 original tweets about the incident sent during and immediately after the perceived crisis.

What they found was that people's tweets about the missile crisis could be grouped together into several common themes.

In the first 38 minutes of the event – which was how long it took before Hawaii officials clarified that the first alert had been sent in error – many of the tweets centred around information processing, as people came to terms with the imminent missile threat.

In this period, people wrote things like, "Sirens going off in Hawaii, ballistic missile threat issued. What's happening?", and "Idk what's going on.. but there's a warning for a ballistic missile coming to Hawaii? [expletive]". (The researchers edited out things like emojis and swear words.)

Another theme was information sharing, as users directed messages at specific Twitter handles to disseminate information about the missile. Authenticating the threat was an important theme too, with many people asking "Is this missile threat real?", and "Where is news about the ballistic missile inbound to Hawaii?".

Of course, emotional reaction was a huge feature of these early messages as well. Some examples include: "there's a missile threat here right now guys. I love you all and I'm scared as [expletive]" and "Woke up and started crying after seeing the Hawaii missile alert. Called my parents and balled [sic] my eyes out because I was so worried."

Once Hawaii authorities revoked the alert and indicated it had been sent out mistakenly, with a second SMS alert ("There is no missile threat or danger to the State of Hawaii. Repeat. False Alarm.") the tenor of the tweets about the incident changed significantly.

In the next 38 minutes (a time window chosen to reflect the same amount of time as during the live crisis), several tweets reflect denunciation: anger and shock that the emergency warning system could screw up so badly.

"How do you 'accidentally' send out a whole [expletive deleted] emergency alert that says there's a missile coming to Hawaii and to take cover. AND TAKE THIRTY MINUTES TO CORRECT?!?" one person tweeted.

Another wrote: "To the person in #Hawaii who sent out that false alarm alert message about missile attack TO EVERY [expletive] CELL PHONE…MOVE TO ANTARCTICA NOW! [emojis] #that[expletive]scaredeveryone @Hawaii_EMA".

At the same time, other Twitter users were expressing how they felt they had insufficient knowledge to act during the emergency, not having a set response plan to the threat of a nuclear emergency.

"[My] friend & i were running around the hotel room freaking out because HOW DO WE TAKE SHELTER FROM A [expletive] MISSILE?!" one person said.

"Can you imagine waking up to an alert that says. 'Take shelter there is a missile on the way' like Bruh. What shelter is there for a missile? That [expletive] might as well say. 'Aye Bruh. Missile on the way. Good luck'," another added.

Others weren't sure the emergency was really over, or otherwise tweeted about mistrust or doubting of the government and the emergency response teams: "And now, should there be another ballistic missile threat, how can we trust it knowing the last one was a grave mistake???".

By looking at how these thousands of tweets spread across the internet, the researchers say it gives us an ability to better understand how people in the Twitter era – most of whom are too young to have lived through the missile drills of the Cold War – react to this kind of emergency alert (even if it's a false alarm).

"The lack of a collective memory of missile alert drills coupled with the present-day ability to instantaneously share information through social media can affect societal reactions," the authors write.

"To improve risk communication, additional research is needed to understand human reactions to emergencies in the social media age so that timely public health messages can be developed and disseminated to save lives."

It's also a case study on how those 38 long minutes when Hawaii believed it was under a possible nuclear attack could have been much less torturous in people's terrified minds – if only the authorities had confirmed the mistaken alert sooner.

"It is critical that public health agencies release communication on social media as quickly as possible after an incident," strategic technology director Tamer Hadi from New York City's Office of Emergency Preparedness and Response, who wasn't involved with the research, told Health Day.

"It is important to acknowledge both what is known and unknown, and follow up consistently from that point on. The longer time that passes without official information, the more time there will be for misinformation and rumours to be exchanged."

The findings are available on the CDC's website.