Mix the syrup, confectioners' sugar, evaporated milk, salt, and butter in a heavy saucepan.
Bring to boiling; set a candy thermometer in place.
Cook over low heat, stirring occasionally, until thermometer registers 234°F.
Remove from heat; remove thermometer.
Add vanilla extract and pecans; stir until mixture begins to thicken.
Set over a pan of hot water.
Quickly drop mixture by spoonfuls onto aluminum foil or buttered waxed paper.
Cool until set, then wrap.