I just banned several hundred IPs being used by a bot attempting to guess passwords of user accounts.
All IPs that attempted to login to 3 or more accounts in the last 24 hours have been IP banned. This may affect some innocent users that happened to be sharing the same proxy or VPN. If your IP has been banned, then you should change your proxy/VPN or contact me to get unbanned (see the contact page for other contact methods if you can't use Danbooru).
I'm still analyzing the situation to determine the scope of impact and if any accounts were compromised.