Why do random communities appear on my instance?

https://random-hero.com/post/29619

Why do random communities appear on my instance? - Random Hero

There have appeared hundreds of communities on my instance I have never searched. Where do they come from? Is it some spam attack? How do I prevent this, and how do I get rid of them?

Do you guys think I should enable captcha?
Uh yes… There are instances (mine included) that’ll automatically defederate you if you have too many users with too few interactions, so better enable captcha if you’re worried about bots.
How do I configure mine to do so? I mean automatic defederation
I made an announcement post for my community here and it has a GitHub link. I think, the repository has a python script that’ll do it.
Suspicious Instances are now being defederated automatically - FOSSware

Hey guys! Thanks to the awesome Lemmy Overseer [https://social.fossware.space/post/20580] (GitHub [https://github.com/db0/lemmy-overseer/]) project and as an effort to block off instances with too lax sign up policies and therefore too many bot accounts, such instances will now be blocked / defederated automatically. FOSSware defederates such instances temporarily, as we believe that the users should decide what they want to see and what not. ✌️

Thanks! I wonder if there’s a script that purges communities that have 0 subscribers on instance