While there is evidence of such incidents, they are perfectly rare and have never resulted in serious injury. Nonetheless, lousy with parents assumed that such heinous practices were Halloween Costume rampant; at the peak of the hysteria, some hospitals offered free x-rays of children's Halloween hauls in layout to find evidence of tampering. Virtually all of the few known candy poisoning incidents involved parents who poisoned their own children's candy, while there have been incidental documents of children putting needles in their own (and other children's) candy in a common bid for attention.
It is not always easy to track the adding to of Halloween in Ireland and Scotland from the mid-seventeenth century, largely because one castaway to trace ritual practices from [modern] folkloric evidence that do not necessarily reflect how the holiday might have changed; these rituals may not be "authentic" or "timeless" examples of pre-industrial times.