If you always had e-mail verification turned on then you can get rid of some of these junk sign-ups relatively easy, I wrote a guide for it here: https://lemdit.com/post/16430
From what I've seen, most of the bot sign-ups that are swelling instance User numbers wouldn't have passed e-mail verification. I think it was done mostly to prove a point, rather than an attempt to actually use those accounts.
Instances that didn't have e-mail verification turned on are in a much harder spot.
If you always had e-mail verification turned on then you can get rid of some of these junk sign-ups relatively easy, I wrote a guide for it here: https://lemdit.com/post/16430
From what I've seen, most of the bot sign-ups that are swelling instance User numbers wouldn't have passed e-mail verification. I think it was done mostly to prove a point, rather than an attempt to actually use those accounts.
Instances that didn't have e-mail verification turned on are in a much harder spot.