In Fischer - Benko, CT 1959, I noted that Kasparov assigned '!?' to Benko's 6...Qb6. The preceding moves 1.e4 c5 2.Nf3 Nc6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 d6 6.Bc4, shown in the following diagram, are known as the 'Sozin Attack'. In the Najdorf Variation, where Black plays ...a6 instead of ...Nc6, Kasparov called 6.Bc4 the 'Fischer Attack'. Fischer played 6.Bc4 in dozens of games against the two variations of the Sicilian.
1959 Candidates Tournament (round 10)
[FEN "r1bqkb1r/pp2pppp/2np1n2/8/2BNP3/2N5/PPP2PPP/R1BQK2R b KQkq - 0 6"]
Kasparov explained his '!?' in a comment on the development of chess superstars.
A rapid ascent in chess undoubtedly generates a number of problems, one of which is the amount and quality of knowledge that is required for a young talent to be able to compete successfully in super-tournaments. An opening repertoire, which has recently served him faithfully in middle-ranking events, proves completely inadequate for play against highly experienced grandmasters. [...] Fischer always worked practically alone. At that time his repertoire was still very restricted, and each of the participants in the Candidates tournament in Yugoslavia tried to exploit this. Thus for the inexperienced opponent Benko had saved up this Queen thrust, unusual for those times.
He also commented that 6...Qb6 was 'A new more interesting way of avoiding the usual variations with 6...e6 than 6...Bd7.' Gligoric had played 6...Bd7 against Fischer in round 4 of the same event, losing in 32 moves. On 6...Qb6, Fischer remarked, 'By putting immediate pressure on the center, Black forces the Knight to a passive post.'