Yup, it's a variation of the closed sicilian known as the King's Indian Attack. White basically plays a King's Indian defence (normally an opening for black) as white. The idea is that white can usually play his first few moves without worrying about black's response. He sets up a kingside fianchetto with g3, Bg2, Nf3 (or Ne2) and then 0-0.

If black responds with his own kingside fianchetto (g6, Bg7), then white usually follows with Bf4/ Bg5, Qd2 and Bh6, to winkle the black bishop away from g7. Then chuck pawns and pieces at the black king until he dies. In some lines, white doesn't castle and combines the Qd2/ Bh6 idea with h4, h5, h6 supported by the Rh1. Great fun.

Otherwise, white can attack the centre with f4 or attack the queenside by clearing the centre of pawns and opening a path for the Bg2.

The problem with the KIA is that it can be a little too formulaic. If black knows what he is doing, he will use one of the anti KIA strategies, such as late castling or a queenside pawn push with moves lije Rb8 and b5, b4.

The other common way for black to combat the KIA is to play e5. That is why many KIA players wait until black has played e6 before playing d3, as Fischer does here. True, black can still push e6-e5, but this wastes a move compared to playing e5 in one go.

If black had played 2...d6, then Fishcer would almost certainly have followed with 3. d4 and an open sicilian.

Not so "early" in this case... This game is from 1970 (and the ones below from the late 1960s). But true, this is a KIA, and Fischer did have a soft spot for it. I remember seeing this game and other Fischer's KIA games with my teacher more than 20 years ago. Here's another "classic":

Fischer vs Myagmarsuren, 1967

And, while not quite a pure KIA, this game has similar attacking themes:

Indeed, the first comment in MSMG is "This used to be my favorite. I thought it led to a favorable variation of the King's Indian reversed, particularly after Black has committed himself with ...e6".

Discovered by you, or by Rybka?

"For a year and a half from mid-1956 his favourite opening complex was the Kings Indian Reversed (which later became known as the King's Indian Attack). The attraction of the opening was obvious - he was so taken by the flexibility of the King's Indian Defence that it was most appetizing to have the same set-up with a move in hand. At Oklahoma City in five out of six games with White Fischer opened in this way. He would play 1. Nf3 2. g3 3. B-g2 4. 0-0 5. d3 6. Nbd2, followed by e4 and expansion in the centre or on the Q side. But although his results with this system were generally impressive (the opposition was none too strong), the positions that he obtained from the opening were not."

And later ...

"He [Fischer] noticed that Black's defensive set-up was much less flexible when the second player had included e6 in his opening moves, and that this move weakened black's f6 square, rendering him more vulnerable to an attack on the dark squares. So from time to time, Fischer employed his King's Indian Attack against the French defence or after the sequence "1. e4 c5 2. Nf3 e6, and it is in this form that the system became internationally popular during the mid 1960s."

So when Fischer talks about the KIA being a favourite, I think he is referring to a time when he played it against anything, especially as a pure KIA starting with 1. Nf3. It is not surprising that he would still roll it out in 1970 against relatively weak opposition, as the KIA is fairly easy to play ... as comfortable as pulling on an old pair of slippers.

If by you, then I applaud you! But with no supporting analysis from you, I'm thinking you meant Rybka found it.>

I would not have seen 28.Be4, not in this lifetime. Further, playing the black pieces, I would have snatched it up.