World number one Garry Kasparov and computer program Deep Junior crouched their pieces and pawns in defensive formations on Sunday to draw the fourth game of their six-game chess match in New York.

Kasparov, taking no chances after losing the third game last Thursday, and his opponent established a so-called ‘hedgehog' opening with their pawns shielding their pieces that led to cautious play.

The Azerbaijan-born Kasparov, 39, considered to be the greatest player in the history of the game, and Deep Junior now have two points each with the fifth game on Wednesday and the sixth and final game on Friday.

"Garry wants to win the match and I think that in game five he is going to put it all on the line when he has the white pieces," US Grandmaster Yasser Seirawan said.

The Russian grandmaster, following his stinging loss to the IBM supercomputer Deep Blue in 1997, has vowed revenge for humanity against the machine in this match at the New York Athletic Club.

The software program, built by Israelis Shay Bushinsky and Amir Ban, and Kasparov played the longest game yet of the match that began a week ago, grinding out 61 moves in more than five and a half hours play.

Kasparov and the programmers agreed to share the point in an endgame that was theoretically drawn even though Deep Junior had three pawns to Kasparov's two and each side had both rooks and a king.

The contest is the first human against computer match under the auspices of the International Chess Federation, known by its French acronym FIDE. It is billed the ‘FIDE Man v Machine World Championship' and has a prize fund of $1 million, including a $500,000 appearance fee for Kasparov.

The games are being shown as they are played on the Web sites http://www.x3dworld.com and http://www.chessbase.com.

Last October, world champion Vladimir Kramnik tied his eight-game match against a German-built program called Deep Fritz in Bahrain. Kasparov is still ranked number one ahead of Kramnik in the FIDE ratings, despite losing his world title to him in London in 2000.

Deep Blue was custom-built to play chess, a 1.4-ton refrigerator size machine with 418 processors that looked at 200 million positions per second. IBM retired Deep Blue after the 1997 match in New York.

Deep Junior is a software program running on eight processors which calculates 3 million moves per second and evaluates positions better than Deep Blue did. A single processor version of Junior was commercially released two years ago and can be bought for about $50 to run on a PC.