Meta (owner of Facebook, Instagram & WhatsApp) is joining the fediverse very soon and have to seriously prepare. This isn’t a theoretical scenario anymore.
“One of Meta’s top executives showed employees a preview of the company’s upcoming Twitter competitor during a companywide meeting today” via https://www.theverge.com/2023/6/8/23754304/instagram-meta-twitter-competitor-threads-activitypub
The photo shows what seems to be a fake conversation with @tonyg with the full @mastodon.social handle visible in two places.
E.g. Fæcebook and Cloudflare IP ranges are public information, your instance’s server can block it by a firewall.