The "Blue Whale challenge" was reported to be an online "suicide game" aimed at teenagers which set 50 tasks over 50 days. The challenge was alleged to be linked to numerous deaths around the world. But little about the "game" was quite as it seemed.
The first tasks were fairly innocuous: "Wake up in the middle of the night" or "Watch a scary film". But day by day, the tasks grew more sinister.
"Stand on the ledge of a tower block."
"Cut a whale into your arm."
The final challenge? A demand that the user kill themselves.
Hundreds of deaths were reported to be linked to the so-called "suicide game".
But closer investigation has revealed something curious. The game, at least as it was initially reported, doesn't seem to have existed at all.
The story of the Blue Whale challenge began with Rina Palenkova.
On 22 November 2015, Rina, a teenager living in south-eastern Russia, posted a selfie.
In the photo she is standing outside. A black scarf is wrapped around her mouth and nose. She is sticking her middle finger up at the camera. It looks like it's covered in dried blood.
The photo's caption read: "Nya bye". The next day, she took her own life.
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Rina Palenkova's death was discussed in a certain type of chat room hosted by Russia's largest social network VKontakte. These forums were places where teenagers met to talk about everyday things like school and which classmates they fancied, as well as darker subject matter: depression, loneliness and suicide.
Scary stories were exchanged. The spookiness of these stories came from how real they seemed, something often achieved through fake pictures or doctored footage.
It is the online equivalent of the claim made by classic horror films that they are "based on true events". Because at the heart of any good ghost story is a sliver of plausibility.
It was in these groups, where the line between fact and fiction was often blurred, that users posted feverishly about Rina. In some instances, they lauded her for ending her life. Videos purporting to be her final moments were posted online.
But amid the rumours, there was a problem.
"Nobody actually knew the true story behind her suicide," says Daria Radchenko, a senior researcher at the Russian Academy of National Economy and Public Administration who has looked into the so-called Blue Whale challenge.
And shortly thereafter, Rina's story merged with other stories of teenage suicide.
On Christmas Day 2015, 12-year-old Angelina Davydova killed herself in the Russian city of Ryazan. A little over a fortnight later, so did Diana Kuznetsova, a teenager from the same city.
When the parents examined the online accounts left behind by their daughters, they found something curious - the two girls were part of similar online groups.
In these groups were drawings of Rina Palenkova, posts about suicide and numerous mentions of blue whales.
Why blue whales?
There has been much speculation about how whales became linked to suicide in these groups. Some journalists claim it is because whales have been known to beach themselves, a phenomenon that has puzzled scientists. Others say that it is a reference to lyrics from a Russian rock band named Lumen.
It's difficult, of course, to say why certain images particularly resonate. Whales are solitary-seeming, sad-looking animals. They make for good memes. One of the most widely shared images was of a whale flying over a city at night. It captured the spirit of these groups - melancholy and quietly surreal.
But it wasn't until May 2016 that speculation about blue whales and suicide became part of the national conversation in Russia.
An article by journalist Galina Mursalieva in Novaya Gazeta, an investigative newspaper, sent the story into overdrive.
Mursalieva suggested that inside certain online groups, some of them with enigmatic names like "Ocean Whales" and "f57", existed a game.
In this game, so-called "curators" would set players 50 tasks over 50 days. On the last day the user was instructed to take their own life.
The Novaya Gazeta report estimated that 130 children might have killed themselves between November 2015 and April 2016 because of their participation in these groups. It would come to be known worldwide as the Blue Whale challenge.
It did not take long for the story to cause considerable alarm. The governor for Ulyanovsk in western Russia went on television to compare the Blue Whale challenge to the Islamic State group.
Soon the panic spread outside Russia. In Georgia, US, a 16-year-old girl killed herself. It was only later when her family had learned about the Blue Whale challenge that they realised the significance of the metre-high paintings she had finished at school shortly before she died.
They appeared to be of blue whales.
Then came other suicides: a boy named Isaiah Gonzalez, also in the United States, a 19-year-old in Hyderabad in India, and two Russian girls, Yulia Konstantinova and Veronika Volkova. A few days before she died, Konstantinova had posted an image of a blue whale on her Instagram account.
In November 2016, 21-year-old Philipp Budeikin was arrested, charged with inciting teenagers to suicide.
Budeikin appeared to admit culpability. He told Russian media outlet Saint-Petersburg.ru: "There are people, and then there is biodegradable waste. I was cleansing our society of such people. Sometimes I start to think that it's wrong, but in the end I had the feeling I was doing the right thing."
He liked computers and was an aspiring producer of "witch house", an electronic music genre with occult themes. A former psychology student, the impression given by the media was that he had used highly developed tactics to manipulate teenagers into killing themselves.
He said he had created the game in 2013 under the name "f57", combining the sound of the start of his name, Philipp, and the last two digits of his phone number. On 10 May 2017 he pleaded guilty and was sentenced to three years in prison.
'Shivers on my skin'
It seemed like an open-and-shut case. Further investigation, however, has revealed that little about the Blue Whale challenge was quite as straightforward as it seemed.
Evgeny Berg was on his way to work when he first read about the Vkontakte chat rooms.
"It made a strong impression on me. It was May but it was very gloomy. I thought 'Oh my God, there is a man out there who is trying to kill a lot of children in Russia.' And I felt shivers on my skin."
Berg, an investigative journalist at Meduza, a Russian-language independent media organisation, decided to dig deeper. His research took him to Sergey Pestov, the father of one of the girls who died around Christmas 2015.
After his daughter's death, Pestov and his wife founded an organisation called Saving Children from Cybercrime. They produced a brochure. It implied that foreign intelligence might be to blame for their daughter's death and that operatives were destroying the Russian people by inciting their children to suicide.
Pestov became a key source of statistics for the original Novaya Gazeta piece.
"He used media sources and open sources to count a bunch of cases all over Russia which were, in his opinion, connected with suicide groups," says Evgeny Berg. "And this number was 130."
This is the same number that was first quoted in the Novaya Gazeta piece. "So that's where the number started" says Berg, "with the father of a girl who tragically died at the end of 2015."
In a story shrouded in rumour and hearsay, this 130 figure is one of the very few widely reported "facts". But even though it is still being used by many news outlets, the figure is tenuous. According to Evgeny Berg and Meduza, it originates with a parent trying to unravel the reasons behind a personal tragedy.
The Novaya Gazeta article has been viewed over one and a half million times, according to the paper.
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We took Evgeny Berg's allegations - that the foundations of the Novaya Gazeta article were, at best, unsteady - directly to the reporter, Galina Mursalieva. She rejected the claim that her report relied on a single flawed statistic.
"This number 130 wasn't based on the conclusions of one father who lost his child," says Mursalieva. "No. This is absolutely wrong. It was based on the conclusions of over 200 parents who lost their children. The father of the girl who died just helped during that period of time. I don't have any reason not to trust them. I checked many things."
Mursalieva had worked on the story for months and included interviews with the parents of deceased children and experts in law and psychology. She says she published it because she wanted to spur into action investigators who she thought weren't taking the problem seriously enough.
But despite the considerable column inches dedicated to the "challenge" over the years, not a single suicide has so far been proved to be linked to these groups, neither by journalists nor police.
"There have actually been way more than 130 cases," claims Mursalieva. "But tell me - who could confirm that this happened? How can it be confirmed?"
That seems to be the crux of it. How can the cause of a suicide ever be "proved"? It might be more accurate to say that teenagers suffering from depression, some of them suicidal, could be drawn to groups that deal with that topic. These same children may use similar images, like blue whales, to articulate their feelings online.
Blue Whale: Fact or Fiction?
With its surreal memes and creepy stories that blur fact and fiction, the subculture of teenage messaging boards is easy for adults to misinterpret. It is possible that journalists and concerned parents accessed these groups and brought together disparate elements into a story that wasn't really there.
That reading tallies with the findings of Alexandra Arkhipova, a professor in Folklore Studies at the Russian State University for the Humanities. When she and her colleagues entered the online groups alleged to be connected with the Blue Whale challenge, they found something strange.
"All of these 'curators'," says Arkhipova, "turned out to be children aged 12 to 14."
Far from being manipulative adults, all the curators seemed to be just kids who had read or heard about the game. In fact, Arkhipova's research suggests that the "challenge" might not have really existed in any substantial way before the Novaya Gazeta article was published.
Arkhipova says that the "curators" she came across online were copycats, acting out step by step the parts of a game that was being widely reported in the press.
"In all these groups people, mainly young people, were waiting for this game," says Arkhipova. "This game never starts."
But where does that leave the story of Philipp Budeikin, the man who confessed to creating the game? Oddly, it might have something to do with his music career.
Friends of Budeikin, speaking to the investigative journalist Evgeny Berg, disputed the claim that he is an evil mastermind.
In fact, they say that he filled online groups with "shock" content related to Rina Palenkova and suicide in order to get as many followers as possible - and then advertise his music.
It is a common practice on VKontakte, where people exploit access to a large amount of followers to advertise other projects or sell products.
When Budeikin was arrested, there were 15 charges against him. By the following month, all but one had collapsed.
The truth at the heart of the Blue Whale challenge is surely both more sad and more mundane than the breathless articles might have us believe. Russia's suicide rates are high especially among the young. It has one of the highest rates of adolescent suicide in the world.
Yes, some teenagers appear to have been drawn into online forums where suicide was being discussed. And in those forums, blue whale memes were being shared. But the idea of a sinister game, one that slowly roped in vulnerable teens and led them down an increasingly tortured path to suicide, seems to be a simplistic explanation for a complex problem.
There is no silver bullet for tackling suicide amongst teenagers. Nor is there a bogeyman that can be locked up to prevent it.
Do you have a story for us? Email BBC Trending.
Story by Ant Adeane
With reporting by Olga Robinson, BBC Monitoring
If you need support for mental health issues, advice is available via the BBC Action Line.
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