Scandal has erupted in the World Chess Federation Championship Showdown with one grand master's secret preparation dramatically leaked for all the world to see.

The 2018 world championship between American Fabiano Caruana and Norway's Magnus Carlsen was plunged into controversy after a since-deleted video appeared to reveal tightly concealed secrets from the American challenger's preparations.

Tongues across the chess world have been wagging since a video of Caruana's pre-series training strategies were loaded on YouTube on Tuesday night ahead of the finalist's fourth match showdown in London.

With their world championship series locked at a stalemate of three draws from the opening three matches, the series was thrown off the tracks heading into their fourth meeting at The College of Holborn.

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Players preparing for a championship series traditionally lock themselves away in secret training camps where they are surrounded by trusted fellow grand masters.

The circumstances of the training camps are closely-protected secrets with even the details of the training partners involved kept hidden for fear of information leaking to a championship rival.

Even the identity of training partners can reveal glimpses about the strategies and mindset of competitors heading into Federation matches.

It's why the event was rocked when a three minute video titled "Today In Chess: World Chess Championship Fabiano In Training" was published by the St Louis Chess Club — where Caruana was rumoured to have trained before the event.

The video reveals the identities of Caruana's training partners and shows him studying strategies in reading material as well as tactical data displayed on a laptop computer screen.

The video has been deleted, but chess reporters have obtained small parts of the published recording.

According to reports, Carlsen's camp have dismissed suggestions the video release could have been a clever piece of espionage or a risky double bluff.

Carlsen's manager Espen Agdestein has reportedly said the leak would make things very uncomfortable for Cuaruana's camp.

"I think this is real," Agdestein said, according to Norwegian journalist Tarjei Svensen.

"It can happen by mistake, and we've been close to making the same mistake. It's more likely that it was a mistake than that it was staged."

The veteran Norwegian champion himself laughed off his opponent's intel leak.

"Well, I'll have a look at the video and then make up my mind," Carlsen said with a dry smile after the game four draw.

"We'll see then."

Meanwhile, grandmaster Jon Ludvig Hammer has told Norwegian media that Caruana must be concerned about the leak.

"This is the opening library of Caruana," Hammer said.

"This was so much detail and in-depth information on an opening he has already used in the world championship match.

"It is obvious that this is relevant."

Game four of the series was also drawn, leaving the world championship battle locked at 4-4 from four games with players needing to reach a score of 6.5 to secure the world title.