Remove all unpopped kernels from popped corn. Place popcorn in a greased 17x12x2-inch baking pan. Keep popcorn warm in a 300 degree F oven while making apricot mixture.
Butter the sides of a heavy 2-quart saucepan. In the saucepan combine the 1 cup butter or margarine, sugar, water, and corn syrup. Cook over medium heat to boiling, stirring constantly with a wooden spoon to dissolve sugar. This should take 7 to 8 minutes. Avoid splashing mixture on sides of pan. Carefully clip candy thermometer to side of pan.
Cook over medium heat, stirring occasionally, until thermometer registers 255 degree F, hard-ball stage. Mixture should boil at a moderate, steady rate over the entire surface. Reaching hard-ball stage should take 10 to 15 minutes.
Remove saucepan from heat; remove candy thermometer from saucepan. Quickly add snipped dried apricots, pecans, and vanilla; stir until well combined. Pour apricot mixture over the popcorn; stir gently to coat popcorn. Bake in a 300 degree F oven for 15 minutes; stir. Bake 5 minutes more. Turn popcorn mixture onto a large piece of foil. Cool completely. Break popcorn mixture into clusters. Store tightly covered. Makes about 10 cups.