Metropolitan Police counter terrorism officers stopped a 16-year-old girl from London travelling to Syria after she was groomed on Twitter to flee to the war zone and marry an Islamic State (Isis) soldier.
An investigation by the Daily Mail revealed the "friendly and innocent" east London schoolgirl was just days away from leaving her family home for Syria, where her older sister travelled last year and had become a recruiter for the terror group.
It was only when the older sister tried to persuade an undercover reporter from the newspaper to join her sister that the plot failed and the journalist handed their information to the Met.
Measures have now been put in place with the girl's family and local authorities to keep her from harm.
Commander Richard Walton of the Met's Counter Terrorism Command said the luring of the schoolgirl was an example of how quickly vulnerable people can become radicalised.
"This case is a frightening example of how quickly social media can be used to groom vulnerable young people," Walton said.
"If the reporter had truly been a 16-year-old girl it would only have been a matter of weeks between the creation of a Twitter account to travelling to Syria.
"This is a stark reminder to parents and the community of the speed with which these cases can develop."
The failed attempt comes after three Bethnal Green Academy schoolgirls ran away from home in February to travel to Syria.
Shamima Begum, 15 – who used the passport of her 17-year-old sister Aklima to travel – Amira Abada, 15 and Kadiza Sultana, 16, disappeared after boarding a plane from Gatwick airport to Turkey on 17 February.
The girls, who were seen on CCTV at a UK airport and in Turkey before slipping over the border into Syria, have reportedly been on the run from husbands they married in the country.