A suspected terrorist attack in Westminster, London, which saw a car plough through a crowd of pedestrians and a man armed with a knife shot by police has the UK's capital in shock and parts in lockdown. As an investigation gets underway, is it possible the event was predicted on the internet a day before?

It sounds like the stuff of conspiracy theorists – but an eerie post on online message board 4Chan from an anonymous user on 21 April contained a cryptic series of dots and dashes that led to a series of clues. Closer inspections revealed the message was Morse code, which if put through a translator directed you towards a Pastebin post full of Binary code.

Sleuths who put the binary code through a Binary-to-text translator generated a set of co-ordinates. Those co-ordinates dropped a pin directly next to Big Ben, off Westminster Bridge. At the time, it meant nothing to anyone, but we now know it is where the incident happened. So far, at least four have been killed and several been injured, including police officers.

It's an intriguing series of clues but was this post a clever hoax or was this really a cryptic tip-off to the shocking events that would occur 24 hours later? Many users commenting on the thread claim the original post is real, while others are hugely sceptical. It is too early to tell at this time whether the post has any legitimacy but the nature of the code and the simplicity to crack it does give reasonable doubt.

It's not the first time 4Chan has been in the middle of controversy surrounding terror events. In October 2015, a 4Chan user may have predicted the Oregon school shooting that left 10 dead, including the perpetrator Christopher Harper-Mercer. A cryptic message appeared on the site the night before that read: "Some of you guys are alright. Don't go to school tomorrow if you are in the northwest. happening thread will be posted tomorrow morning. so long space robots."

Again, as with the nature of 4Chan, which hosts controversial message boards such /pol/, there was an air of scepticism around it. Some believed the post to be real, with even the possibility of the OP (original poster) to be Harper-Mercer himself.

As the investigation into the London attack continues we will update this story when we hear more about the legitimacy of the post, or whether it's just another case of a 4Chan troll.

Scotland Yard said it is treating the Westminster attack as a terrorist incident and is appealing for any visual material of the incident, which should be passed on to http://www.ukpoliceimageappeal.co.uk.