The Brown Marmorated Stink Bug is a native of China, that was probably accidently introduced to the eastern US (Pennsylvania) in the late 1990′s. It has become a serious pest of fruit, vegetables and agricultural farm crops in the mid-Atlantic region.
They are attracted to the sides of houses in the fall when they are looking for sheltered overwintering sites. They gain entry through cracks around doors, windows and vents. They may spend the winter in walls and appear again in the spring.
While they are not harmful to people, their size makes them quite alarming when they fly around indoors. Their name comes from the unpleasant odor released when they are crushed.
Follow the link here for more information on the Brown Marmorated Stink Bug.