If you ask a chess player what opening is the most dangerous one in the sense that you can lose quickly if you don't know exact moves you are supposed to play, then most probably you'll hear the King's Gambit, the Sicilian Defense or some other notoriously sharp opening. My personal choice would be the Hanham variation of the Philidor defense (1.e4 e5 2. Nf3 d6 3. d4 Nd7). If you read 'My system' by Nimzowitch then you might be surprised by my choice, since the Hanham variation was Nimzowitch's favorite weapon to reach the positions where a long positional struggle ensued. Yet, this variation is a real minefield. We all learn pretty quickly that the f7 pawn is Black's weakest spot in the initial position. I don't know any chess player who hasn't succumbed to the Fool's Mate (Bc4, Qh5 and Qxf7 checkmate) or the Fried Liver Attack. But if you really want to see how the attacks against the f7 square go in the open games, look no further then the Hanham variation! So, today's typical pattern we are going to learn is "combinations and traps on the f7 square".
The first combination/trap happens as early as move four!
So, the natural looking 4...Ngf6 move was a mistake. Let's try 4...Be7 instead, defending against possible Ng5 threats.
OK, it turns out that 4...Be7 is not good either. So how about 4...h6 then, preparing Ngf6 development?
Even if Black plays the best theoretical move 4...c6, he is not completely out of the woods yet as the next game demonstrates.
Now you can see why in the modern tournaments Black frequently uses a different move order to reach the Hanham and also to set up a nasty trap.
In the next position you should decide if you want to start an attack by 6.Bxf7 followed by 7.Ng5+
But even this modern, sophisticated move order doesn't guarantee against surprises.
As you could see, the fight in the games that we have analysed today revolved around the 'magical' f7 square. We witnessed different methods White can use to assault this weakest spot in the Black position. Even if you don't play the Philidor defense but answer 1.e4 with 1...e5 you must know these typical ideas in order to avoid potential disaster in your own games!
Good luck!