I'm terribly sorry for today's downtime. We are now back.
Post-mortem:
Yesterday my hosting provider, Hetzner, received an abuse report for our entire IP due to a user account that apparently was used as a botnet controller. I suspended the account immediately, but forgot to submit a statement to Hetzner.
After 24 hours, the IP to mastodon.social was locked by Hetzner. I've reached out to them as soon as I learned of this.