How did Tom Riddle find out about what Horcruxes were and what they did before he asked Horace Slughorn?

Hermione wasn't about to find a single thing about them in the library when Harry brought it up and she had never heard of them prior. Where else would Tom have heard of them?

marked as duplicate by Himarm harry-potter Jun 24 '17 at 0:21

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.