Combine sugar, water, corn syrup and salt in a 4 cup glass measuring cup. Microwave on high, uncovered for 3 minutes. Stir and insert microwave thermometer. Microwave 6 to 8 minutes, until thermometer reaches 250 degrees. While syrup cooks, beat egg whites until stiff peaks form. Pour hot syrup in a very slow thin stream into egg whites while beating at high speed. Continue beating until candy begins to lose its gloss and holds shape. Beat in vanilla and stir in nuts. Drop by spoonfuls onto waxed paper and allow to set. Yield: 3 dozen pieces