I'm involved in a facebook forum which has recently hit 100,000+ members. Even with that size it'll go for a while without bots and spammers, but then there will be a spate of them, and all three admins are busy for a day or two zapping them. Most we zap are far-right political activists, some claiming to be Irish, but the vast, vast majority of whom seem to emanate from the USA (extremist trump supporters, extremists racists and religious cranks) and the UK (tommy robinson / racist types).
Some are identifiable straight away and don't get in. Others appear to answer all the entry questions properly and have good reason for entering, then start their nonsense. So, out comes the Zapper!
Tis the world we live in..............! Gawd forbid, we'll be getting people here who aren't railway enthusiasts next! Horror of horrors!