A novelty is a move or idea in an opening system that has never been tried before. As a semi-aggressive 1.e4 player myself, I can't stand playing against the Petroff's Defense, a seemingly unbreakable system. In 1998, however, hope was renewed by a master named Csaszar who came up with a brilliant novelty in one of the lines.
Even until now, black has still not found an adequate response to 9.h3!? Let's investigate some of the lines. 9...Bh5 is the only logical continuation.
Although Csaszar continues with the normal 10.c4 and retains good chances in the game, here I recommend 10.g4! This move does weaken the kingside pawn structure, but ironically enough, the white king is never really in serious danger.
Black is then confronted with two choices once again. He must retreat the bishop either to f7 or g6. The move 10...fxg4 is followed easily by 11.Bxe4 after which black will find himself in loads of trouble.
Therefore, the two pertinent lines are 10...Bf7 11.gxf5 0-0 12.Ne5 Qf6 13.Nc3 Nxc3 14.bxc3 Nc6 15.Nxc6 (not 15.Nd7? Qh4 16.Qg4 Qxg4 17.hxg4 Rfe8 and the white knight is no longer valuable on d7) bxc6 16.Qg4 when white is posed for a strong kingside attack up the g-file.
The retreat to g6 seems to be better, but it leads to a more dynamic position. 10...Bg6 11.gxf5 Bxf5 12.Ng5 0-0 13.Nxe4 dxe4 14.Bxe4 Qh4 15.Bxf5 Rxf5 16.Re8+ Kf7 17.Qe2 when black will be able to regain his pawn, but the white pieces will soon reveal the discomfort of his king.
This relatively recent innovation gives white a chance to play more aggressively against an otherwise fortress of a defense.