After thanking the girl for returning her purse, she tells her not to go to back to the shopping centre this week, warning her there will be a car explosion. In a bizarre, somewhat eerie and rather unfortunate coincidence, a car was engulfed in flames at Chadstone Shopping Centre on Thursday amid the Christmas rush. The rumour mill went into overdrive across social media. "I got this story three days ago from a family friend whose daughter’s best friend knew the girl this happened to," wrote one Reddit user.

But not everyone was buying into it. "Haha no way," Reddit user DonBlasto said. "That's been going round since the '80s in the UK. Back then it was a fear of IRA bombings though." Soon after, variations of the story were lighting up the screens of smartphones across Melbourne as teenagers discussed the hoax in the confines of their online group chats. It evoked such a sense of fear in some Melburnians that police were compelled to issue an official statement that there was no veracity in the story.

"Police are aware of comments on social media which references remarks in regard to a shopping centre in Chadstone," police tweeted on Tuesday. "Similar comments have been received in the past and are not being treated as credible." Loading The car fire damaged 11 other vehicles parked nearby and sent part of the shopping centre into lock-down. Police were quick to respond, releasing a statement that the fire was non-suspicious and deemed accidental due to a vehicle fault.

But that didn't stop the wild conspiracy theories circulating on Twitter. So where did this tale, often dubbed the 'grateful terrorist', originate? Well, it's hard to say. Wild and morphed variations of this rumour have existed for years, with some believing it gained traction after the September 11 terrorist attacks in 2001.

Since then, there have been warnings not to drink Coke after a certain date or not to take the Tube in London. In one case, the New York Police Department issued a statement calling for calm saying there was no basis to the rumour after people became fearful of travelling to Manhattan. In these hoaxes, the warning comes from a stranger who is almost always Muslim or of Middle Eastern descent. The urban myth gained momentum following the death of al-Qaeda leader Osama bin Laden in 2011, when the chilling “helped terrorist” trope gripped Paris. In that version, a supposedly grateful terrorist rewarded a man who had returned his dropped wallet to him with the advice not to use the Paris Metro the next day because an attack was going to take place.