By Agence France-Presse How did an internet hoax about kidnappers driving white vans lead to "collective hysteria" and near-lynchings in the Paris suburbs this week? Experts say it is a combination of old-fashioned prejudice and modern technology. Around 20 people were arrested on Monday night after gangs of vigilantes attacked camps of ethnic Roma people in northeast Paris after false reports that they were responsible for abductions in the area using white vans. One senior police officer in the area had issued a written warning earlier in the day saying that a form of "psychosis" had set in as people shared warnings on messaging services such as Snapchat and WhatsApp and social media like Facebook. "There's a Romanian network of organ traffickers. They're everywhere in the suburbs," wrote one user in an online post above a picture of the ubiquitous white van, a common sight on French streets. During a court hearing on Wednesday, where three suspected vigilantes aged 18 to 21 appeared before magistrates, public prosecutor Denis Fauriat referred to "collective hysteria." The violence, which recalled similar incidents in India, Brazil and Mexico in recent years, again underlined the difficulty for governments in controlling the flow of false information in today's hyper-connected world. But like many online hoaxes -- or offline rumor-mongering -- the warnings bring to mind some infamous cases from the past, making them sound plausible. - Unverified information - Aurore Van de Winkel, an academic who tracks urban legends and hoaxes, says French people are still traumatized by the serial killers Marc Dutroux and "the Ogre of the Ardennes" Michel Fourniret who used white vans to abduct their victims. "There have been real cases," she told AFP. "People want to protect their loved ones with a click of the mouse, as they used to do in person, so they share the information. They're bombarded with information and they don't verify it." Warnings about white van kidnappers have been documented in France since at least 2011 in the Drome area of south-east France, the central Loiret region and the Pas-de-Calais area in the north among others. They usually entail a message warning about suspicious people approaching children or women and include a picture of a van, or a first-person account from someone recounting how a family member or friend has gone missing. The phenomenon became so widespread that French satirical website Le Gorafi published a joke article in 2013 entitled "the suspicious man in a white van who asked for directions from some children was just asking for directions." Old prejudices, new twist  But experts say darker forces of prejudice and racism are at play, which are nothing new but has been supercharged by the internet and modern communications. In 1969, French author Edgar Morin published a book called "The Rumour of Orleans" which recounted the origins of stories in which young women were said to be disappearing at clothing shops owned by Jews in the central French town. Speaking this week, he saw a parallel with the attacks in Paris on ethnic Roma people, some of whom saw their vans set on fire and their families terrorized by mobs carrying petrol cans and metal bars. "In both cases, the rumor is about a minority which is seen as having something mysterious and worrying about them," he told Le Parisien newspaper. "It taps into things which are anchored in our beliefs and prejudices, i.e. that the Romas are thieves," he added. Communities of Roma people have lived in France for centuries, but tens of thousands more moved from Bulgaria and Romania in southeast Europe after the countries joined the EU in 2004. The traditionally nomadic people, who are sometimes called Roms or gypsies, are thought to number around six million in the EU and are considered to be the bloc's largest and poorest minority, according to the Council of Europe human rights body. 'Tipping point'  Rumors of kidnappings spread on phone messaging service Whatsapp led to the deaths of 30 people in India last year, including a transgender woman and an elderly woman who handed out chocolates to children. A Brazilian woman died after being beaten in the street in the coastal town of Guaruja, near Sao Paulo, in 2014 over false Facebook rumors that she abducted children for witchcraft rituals. "I think we're at a sort of tipping point. We're seeing the direct effects of violence and hate speech that is spread on the internet," said Marie Peltier, an academic at the Haute Ecole Galilee in Brussels who has written a book about conspiracy theories. "We're seeing more and more cases of theories propagated on the internet crossing over into real life," she told AFP.