Until a few days ago, most Chechens in the United States lived largely anonymous lives. Few Americans even knew what and where Chechnya was. Now, two Chechen brothers are at the center of one of the most serious terrorist attacks on the United States since Sept. 11, 2001. While the motivations behind the bombings are still unknown, the attack has made Chechnya a focus of American scrutiny, and it has thrust Chechens living here into an unwanted spotlight.