Deep Blue's cheating move

by Albert Silver
2/19/2015 – It is a sign of just how impactful the famous Deep Blue match against Kasparov was in 1997, that 18 years later, books come out citing it still, and magazines such as Time cast their eye on it even today. Here we take a close look at the most controversial move from game two, that prompted Kasparov to accuse the Deep Blue team of cheating. The results may surprise you.

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Nearly two decades later, the match still fascinates

This week Time Magazine ran a story on the famous series of matches between IBM's supercomputer and Garry Kasparov. The subject was a few of the moves that stood out for a variety of reasons, such as a bug in game one of the 1997 match, and a move in game two that Kasparov found so unbelievable that he accused the Deep Blue team of cheating. The allegation was that a grandmaster, presumably a top rival, had been behind the move.

In fact, grandmaster Yasser Seirawan told Wired in 2001, “It was an incredibly refined move,
of defending while ahead to cut out any hint of countermoves, and it sent Garry into a tizzy.”

The topic of analyzing some key moves by Deep Blue with a top engine was recently covered at ChessBase News in a series of three articles:

Komodo 8: Deep Blue revisited (part one)

12/26/2014 – When Garry Kasparov faced IBM's super computer Deep Blue, there was not a player alive who did not secretly dream of having their own private Deep Blue to consult on demand. That day has already come and passed as today's engines such as Komodo 8 can outperform the famous computer even on a smartphone. Here we take a look at the famous match and key moments.

Komodo 8: Deep Blue revisited (part two)

12/31/2014 – The first two games of the titanic match between the world's strongest player versus the world strongest chess computer showed significant changes. While the computer played moves that baffled humans, the number of moves a grandmaster would outright scoff at were dwindling and could only be judged as eccentric. Today's best engines are actually no different, just stronger.

Komodo 8: Deep Blue revisited (part three)

1/9/2015 – Nearly eighteen years later, the matches between Garry Kasparov and Deep Blue continue to stir the imagination and fascination of people around the world. It has inspired books, documentaries, and theatrical productions. Looking over the games with a top engine such as Komodo 8, and comparing with the computer logs, sheds new light, and even reveals a missed win by Kasparov.

However, the purpose had been to highlight refinements and revelations uncovered with modern hardware and chess engines, and since there had been no disagreement with the so-called cheating move, it was not mentioned. So the engines agree with Deep Blue's choice, is that all? Not quite. Let's take a look at the controversial moment first.

This was the position on the board after 35 moves. It is White to play.

Before trying to simply guess what was played, if you don't already know, it is important to remember that the year is 1997, and engines, and even supercomputers, played quite a bit differently than today's uber-engines. They were notoriously materialistic, and a tactic used by a player such as Kasparov, who would get deep into the head of his opponent, was to bait the machine with a 'poisoned pawn', allowing him to direct the game in a direction of his choosing.

The pawn on b5 is clearly weak, and it should not be hard to bring it crashing down. The problem is that the most direct method is far less than optimal. As noted by grandmaster John Nunn, who annotated the game then and whose notes can be found among the tens of thousands of commented games in MegaDatabase:


[Event "New York Man-Machine"] [Site "New York"] [Date "1997.05.04"] [Round "2"] [White "Deep Blue"] [Black "Kasparov, Garry"] [Result "1-0"] [ECO "C93"] [BlackElo "2785"] [Annotator "John Nunn"] [SetUp "1"] [FEN "r1r1q1k1/6p1/p2b1p1p/1p1PpP2/PPp5/2P4P/R1B2QP1/R5K1 w - - 0 36"] [PlyCount "6"] [EventDate "1997.05.??"] [EventType "match"] [EventRounds "6"] [EventCountry "USA"] [Source "ChessBase"] [SourceDate "1997.11.17"] {It would be wrong to play} 36. Qb6 Rd8 (36... Bc7 $2 37. Qe6+ Kh7 38. Qxe8 {wins}) 37. axb5 Rab8 38. Qxa6 e4 {when, at the cost of two pawns, Black has developed considerable counterplay based on ...Qe5 and possibly ...e3. However, this is again a remarkable move by Deep Blue; most computers (including Fritz and Hiarcs) go for the material without hesitation. Did Deep Blue reject this line based on very deep analysis, is there some subtle programming involved?} 1-0

Needless to say, Deep Blue did not follow the trail of bread crumbs Kasparov was carefully sprinkling in its path. It played the very strong 36.axb5! axb5 and 37.Be4! to which Nunn comments, " A cruel move. Black's only chance of counterplay is to activate his bishop by ...e4, but Deep Blue cuts the rope which might have saved the drowning Kasparov."

In fact, if you consult any of the top engines of today, whether it be Houdini 4, Stockfish 6, or Komodo 8, they all choose Deep Blue's move 36.axb5. For example:

Komodo 8: 36.axb5 axb5 37.Be4 Qd8 38.Kh2 Rcb8 39.Ra6 Kf8 40.R6a5 Kg8 41.R1a2 Rxa5 42.Rxa5 Bc7 43.Ra1 Bb6
+/- (0.84) Depth: 29 00:02:15 686MN, tb=57

The problem is that it does not condemn 36.Qb6 either, just the blind pawngrabbing that follows. That very same Be4 can be combined with it to great effect. So what does this all mean? It means that while 36.axb5 was indeed a very strong move, it was not the only one, and the move order was not actually essential so long as the ideas are maintained, and, as pointed out by Nunn, White avoids allowing Black the time to strike back with ...e4 himself.

Analysis with the top engine lines:

[Event "New York Man-Machine"] [Site "New York"] [Date "1997.05.04"] [Round "2"] [White "Comp Deep Blue"] [Black "Kasparov, Garry"] [Result "1-0"] [ECO "C93"] [BlackElo "2785"] [Annotator "John Nunn"] [SetUp "1"] [FEN "r1r1q1k1/6p1/p2b1p1p/1p1PpP2/PPp5/2P4P/R1B2QP1/R5K1 w - - 0 36"] [PlyCount "7"] [EventDate "1997.05.??"] [EventType "match"] [EventRounds "6"] [EventCountry "USA"] [Source "ChessBase"] [SourceDate "1997.11.17"] 36. axb5 $1 ({It would be wrong to play} 36. Qb6 Rd8 (36... Bc7 $2 37. Qe6+ Kh7 38. Qxe8 {wins gewinnt}) 37. axb5 ({Komodo 8 64-bit points out that after} 37. Be4 $1 {White will continue to maintain a strong advantage, even after Black's best chance with} a5 $1 ({The tempting} 37... Qh5 $2 {to try to get counterplay with the queen is insufficient and ultimately worse.} { Komodo 8 64-bit:} 38. axb5 Rab8 39. Qxa6 Qh4 40. Re2 Qg3 41. Qa3 Rxb5 42. Qc1 Bc7 43. Kh1 Rbb8 44. Qe1 Qxe1+ 45. Rexe1 Kf8 46. g3 Bb6 47. Ra6 Rd6 48. Rd1 Ke7 49. Kg2 Rd7 50. Rda1 Kd6 51. R1a5 Ke7 52. Ra2 Kd6 53. Ra1 Ke7 54. Rd1 Kd6 55. Kf3 Ke7 {1.80/31}) 38. axb5 axb4 39. Rxa8 Rxa8 40. Ra6 Rd8 41. cxb4 c3 42. Qc6 Qh5 43. Qxc3 Qe2 44. Qd3 Qe1+ 45. Kh2 Kh7 46. Qc4 h5 47. Qd3 h4 48. Qf3 Qxb4 49. Qg4 Bc5 50. d6 Qd4 51. Qxh4+ Kg8 52. Qe1 Rxd6 53. Ra8+ Rd8 54. Rxd8+ Qxd8 55. h4 Qd4 56. Qb1 Qc4 57. g3 Kf7 58. Kh3 Ke7 59. Bc6 Bd4 60. Qe4 Qf1+ 61. Kg4 Qd1+ 62. Qf3 {0.97/31}) 37... Rab8 38. Qxa6 $2 ({Komodo 8 64-bit quite agrees that Qxa6 opens the way for Garry, but sees} 38. Qc6 $1 {as quite winning for White.} axb5 39. Qxe8+ Rxe8 40. Ra6 Red8 41. Be4 Kf8 42. Kf2 Ke7 43. Kg3 Rb7 44. Kg4 Kf8 45. R1a5 Bb8 46. Re6 Kf7 47. Kf3 Kg8 48. Ra1 Kh7 49. Rc6 h5 50. h4 Kh6 51. Raa6 Ba7 52. Re6 Rbd7 53. g3 Bg1 54. Rxe5 {1.82/29}) 38... e4 {when, at the cost of two pawns, Black has developed considerable counterplay based on ...Qe5 and possibly ...e3. However, this is again a remarkable move by Deep Blue; most computers (including Fritz and Hiarcs) go for the material without hesitation. Did Deep Blue reject this line based on very deep analysis, is there some subtle programming involved?}) 36... axb5 37. Be4 {A cruel move. Black's only chance of counterplay is to activate his bishop by ...e4, but Deep Blue cuts the rope which might have saved the drowning Kasparov.} Rxa2 38. Qxa2 {This position is just lost. Black's bishop must stay on d6 to block the d5-pawn, but Black cannot both maintain this bishop and defend the weak pawn on b5. Black's total lack of counterplay is the deciding factor: White has plenty of time to slowly infiltrate with his queen and rook.} Qd7 39. Qa7 {and Deep Blue had a winning advantage.} 1-0

It is clear that while Deep Blue was far ahead of its time, by the time the controversial position arrived, it had more than one path to victory.

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Born in the US, he grew up in Paris, France, where he completed his Baccalaureat, and after college moved to Rio de Janeiro, Brazil. He had a peak rating of 2240 FIDE, and was a key designer of Chess Assistant 6. In 2010 he joined the ChessBase family as an editor and writer at ChessBase News. He is also a passionate photographer with work appearing in numerous publications.