Caramel Popcorn Balls

My mom's recipe.  She made these every year around Christmas and New Years, so we had yummy treats to snack on all through our holiday break from school. They're the perfect treat for Fall, too! We love 'em around here!!!

2 1/4 c. brown sugar
1 can sweetened condensed milk
1 cube butter
1 c. white karo syrup
1 c. unprepared popping corn

Pop popcorn in air popper. Set aside.
Bring sugar, butter, and syrup to a boil. Take off heat and add milk stirring constantly. Place back on heat and cook to full bubbling boil that can't be stirred down, stirring constantly.
Pour over popcorn. Mix well until all the popcorn is coated.
When cool, form in tennis sized balls and let set on wax paper.