The reason I posted this yesterday is that I suspended hundreds of accounts, just as @jerry@infosec.exchange did. And other moderators as well.
Important: this is NOT an issue with Mastodon. Or the fediverse. It’s a common thing that happens when passwords are compromised and folks use the same ones for many or all of their online accounts. Mastodon is simply one of the targets at the moment.
For server admins, Jerry has a script that will reset passwords on dormant accounts. I highly recommend running this on your instance.