I looked at the lemmy stats again today like the last few days (since the 1st of July), apparently tonight there has been another wave of bot signups.:
Lemmy: 1,555,395 overall users (+ 2363)
Kbin: 55,201 overall users (+ 433)
Active last 30 days:
Lemmy: 56,859 users (+ 1142)
Kbin: 55,099 users (+ 331)
^ 2023-07-02 20:15:00 CEST
Lemmy: 2,179,081 overall users (+ 623686, bots)
Kbin: 55,863 (+ 764)
Active last 30 days:
Lemmy: 59,438 (+ 2579)
Kbin: 55,532 (+ 433)
^ 2023-07-03 13:30:00 CEST
Of course “tonight” refers to tonight in central european summer time so it probably was more middle-of-the-day for you.
If you go to the site I linked at the beginning and sort by “Total users” you can see instances with 80000 users and 1 active user for example.
Open signups should be prohibited and affected instances should do something against the botted accounts or defederate. New instances should at the very least start using captchas and email verification.
Probably by the amount of account creations per IP. That would at least be the simplest way. I can understand having alts or inactive accounts but those aren’t the problem, the bots account for probably around 85% or so of accounts by now.