The Irish singer took to Twitter to muse on how "crazy it is" people are able to get away with sending online abuse, some of which has been directed at his young nephew.
"For the last two weeks I've been receiving messages off a group of fans, they have drowned my phone in messages, keeping me awake at night," said Niall.
"But the worst part is. They have been nothing but abusive . Saying things you wouldn't even believe about me and my family. And saying the worst things ever about my little nephew."
Niall, 22, went on to say: "Thank God I'm not the kind of person who thinks into stuff like this. But I just think it's crazy how we let people away with things like this. And the sad thing is . As I tweet this they are in the group chat laughing at me."
He added: "Don't worry about me. I'm the most carefree, laid back person around. But I'm just signalling it, because this sh*te is happening to others."
As you'd expect, Niall was inundated with messages from fans, deploring those sending "abusive" messages, and praising Niall for speaking out.
Among them was YouTube star Alfie Deyes, who wrote: "Love that you're speaking up about behaviour like this man! I see lots of similar things happening & it needs to stop x."