Keep popcorn warm in 250 degree oven.

Cook first five ingredients over medium heat, stirring constantly until mixture comes to a boil.

Continue cooking without stirring until mixture reaches 270 degrees on a candy thermometer or until a small amount dropped into very cold water separates into hard threads.

Add vanilla and stir.

Pour mixture over popped corn, mixing with a fork.

When cool enough to handle but still quite warm, form into balls.