Spray large roasting pan with cooking spray; add popcorn and place in 300║F oven until warm. (Popcorn can also be warmed in a large microwave safe bowl for 1 to 2 minutes on HIGH (100%) power.)
Combine sugar, Karo«, butter and salt in a heavy 2-quart saucepan. Stirring constantly, bring to boil over medium heat. Continue stirring and boil 2 minutes.
Remove syrup mixture from heat; stir in vanilla and baking soda. Pour syrup mixture over warm popcorn stirring to coat well. Cover hands with two plastic bags, spray bags lightly with cooking spray. Working quickly shape twelve 3-inch popcorn balls.
Cool completely. Wrap individually in plastic wrap.