I am purchasing a two story home and the attic is about 1,500 sq. ft. There is an opening through a closet and the 2nd. floor ceiling is insulated fully and is visable in the attic. There is an area of approximately 15' X 20' that has a black mold like covering on the insullation. The rest of the area looks as insulation should, yellow in color. What is the proper procedure to take care of it?