In Harry Potter and The Deathly Hallows, the following words are uttered by Harry Potter before he defeats Voldemort:
“There are no more Horcruxes. It’s just you and me. Neither can live while the other survives, and one of us is about to leave for good. . . .”
Harry Potter and The Deathly Hallows
When he says that, everyone who is in the Great Hall can hear him and there are bound to be some people - most likely adults - who know what a Horcrux is so they won't dismiss the word in the midst of the confrontation. So it is likely that the fact that Voldemort had created Horcruxes and especially more than one, is something that the few who were in the Great Hall know.
But is the whole story something that eventually becomes history? Does the fact that Voldemort created 7 Horcruxes become widely known to people or do the people that were there keep it as hushed as possible?
If it becomes common knowledge, perhaps written in history books and told to young children, wouldn't that make it even easier for dark wizards to get inspired and create their own Horcruxes and even push their limits even further? (As far as we know before Voldemort even the darkest of wizards had created 1 Horcrux). Also wouldn't they learn from Volemort's mistakes and create Horcruxes out of less significant objects?
So how much of the story becomes widely known?