Magnus Carlsen and Fabiano Caruana are no closer to a verdict in their world championship match after playing to a straightforward 34-move draw in Game 4 on Tuesday afternoon in London. There was added spice away from the board, though, as a clip that appeared to reveal tightly held secrets of the American challenger’s preparation was uploaded to YouTube and into the public domain.

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Carlsen, playing with the white pieces, delivered a surprise with the geographically appropriate English Opening, a choice he’d played only once in 37 previous classical meetings with his American rival. A predictable line followed through 10 moves until the Norwegian champion offered a novelty with 11. b4, yet Caruana, who had struggled with time in earlier games, immediately struck back with 11. ... Bd6.

Quick guide World Chess Championship 2018 Show Hide The players Norway's Magnus Carlsen is defending the world chess championship against Fabiano Caruana of the United States. The best-of-12-games match is taking place at the College in Holborn between 9 and 28 November, with the winner earning a 60% share of the €1m ($1.14m) prize fund if the match ends in regulation (or 55% if it's decided by tie-break games). Carlsen, 27, has been ranked No 1 for eight straight years and was considered the world’s best player even before he defeated Viswanathan Anand for the title in 2013. Caruana, 26, is ranked No 2, having earned his place at the table by winning the candidates tournament in March. No American-born player has won or even competed for the world title since Bobby Fischer in 1972. It marks the first title match between the world's top two players since 1990, when Garry Kasparov and Anatoly Karpov faced off for a fifth and final time. The format The match will consist of 12 classical games with each player awarded one point for a win and a half-point for a draw. Whoever reaches six and a half points first will be declared the champion. The time control for each game is 100 minutes for the first 40 moves, 50 minutes for the next 20 moves and then 15 minutes for the rest of the game plus an additional 30 seconds per move starting from move 1. Players cannot agree to a draw before Black's 30th move. If the match is tied after 12 games, tie-breaks will be played on the final day in the following order: • Best of four rapid games with 25 minutes for each player with an increment of 10 seconds after each move. • If still tied, they will play up to five mini-matches of two blitz games (five minutes for each player with a three-second increment). • If all five mini-matches are drawn, one sudden-death 'Armegeddon' match will be played where White receives five minutes and Black receives four minutes. Both players will receive a three-second increment after the 60th move. In the case of a draw, Black will be declared the winner.

The schedule Thu 8 Nov – Opening ceremony

Fri 9 Nov – Game 1

Sat 10 Nov – Game 2

Sun 11 Nov – Rest day

Mon 12 Nov – Game 3

Tue 13 Nov – Game 4

Wed 14 Nov – Rest day

Thu 15 Nov – Game 5

Fri 16 Nov – Game 6

Sat 17 Nov – Rest day

Sun 18 Nov – Game 7

Mon 19 Nov – Game 8

Tue 20 Nov – Rest day

Wed 21 Nov – Game 9

Thu 22 Nov – Game 10

Fri 23 Nov – Rest day

Sat 24 Nov – Game 11

Sun 25 Nov – Rest day

Mon 26 Nov – Game 12

Tue 27 Nov – Rest day

Wed 28 Nov – Tie-break games/Awards and closing The games commence each day at 3pm in London.

The world No 1 created a queenside weakness over the next few moves, but he eschewed any risk in exploiting it and the game appeared bound for a peaceful result after an exchange of queens and bishops (18. ... Bxe4 19. Qxf6 gxf6 20. dxe4).

A series of moves (25. ... Rdc8 26. Rc2 Ra4 27. Kf3) during the final hour exposed vulnerabilities on the b4 and c6 squares that balanced each other out and before long the players agreed to a draw, their fourth in as many games, after less than three hours.

Carlsen and Caruana remain deadlocked in their world title match after Tuesday’s Game 4 draw.

“He seems to have out-prepared me with the black pieces so far so I’ll have to try harder,” Carlsen said in a television interview.

An uncomplicated afternoon of play at the College in Holborn began with controversy off the board early Tuesday morning when a two-minute clip revealing details of Caruana’s top-secret preparation was uploaded to the Saint Louis Chess Club’s YouTube channel before it was quickly taken down, but not before crucial screen shots were captured and disseminated on social media.

Olimpiu G. Urcan (@olimpiuurcan) This morning a 2-minute clip from one of Caruana's training camps was uploaded on YouTube (now deleted). It featured various activities, chess included. Viewers could also see a laptop screen with a ChessBase file laid open. The greatest intel blunder in chess history or a hoax? pic.twitter.com/nwHL75M2cC

The footage included pictures of an open laptop with a list of openings allegedly researched by the world No 2 along with the names of three grandmasters – Leinier Domínguez, Alejandro Ramírez and Ioan-Cristian Chirila – who could potentially be working as seconds in the American’s camp.

The apparently accidental release immediately prompted speculation as to whether it was a ghastly blunder by Caruana’s club – one that would spoil in one fell swoop months of secretive preparation for the €1m ($1.14m) match – or a deliberate misinformation campaign intended to spread false intelligence to the Carlsen camp.

Facebook Twitter Pinterest Attendees play chess at the College in Holborn during Tuesday’s fourth game of the world championship match. Photograph: Facundo Arrizabalaga/EPA

Caruana was polite but terse in declining to comment when asked about the video during Tuesday’s post-game press conference. The champion’s response was somewhat more glib.

“Well, I’ll have a look at the video and then make up my mind,” Carlsen said with a wry smile, prompting laughter from the gallery. “We’ll see then.”

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Carlsen’s manager Espen Agdestein, who initially declined to address the video, later said he believed it was a mistake by Caruana’s camp in a quote reported by leading Norwegian chess journalist Tarjei Svensen.

“I think this is real,” Agdestein said. “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.”

Norwegian grandmaster Jon Ludvig Hammer said he believed the information revealed was authentic, representing a devastating setback to Caruana’s bid to become the first American to win the world championship since Bobby Fischer in 1972.

“This is the opening library of Caruana,” Hammer said on Norwegian television network VG. “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.”

Both players will look forward to Wednesday’s rest day before the best-of-12-games match, the first world title showdown between the sport’s top two players in 28 years, resumes on Thursday with Caruana playing as white in Game 5.