What impact?
As long as you dont go on lemmy.world, it's not going to redirect you to all the stupid websites.
And I doubt whatever they're posting (if they're posting anything) is getting upvoted, so you won't see it anywhere else.
And where are you getting "malware" from?
People are acting like it's some crazy hack, and not the 4chan rejects from exploding heads finally guessing an admins password a week after they got defederated. And after all that time chasing the mailman, they had no idea what to do when they guessed it
But this does highlight an issue with instances. I doubt the handful of admins know each other. Like, maybe an email, but for the most part if shit like this happens during "off hours" it might be a while before the top admin even knows there's an issue