sslh lets one accept HTTPS, SSH, OpenVPN, tinc and XMPP connections on the same port. This makes it possible to connect to any of these servers on port 443 (e.g. from inside a corporate firewall, which almost never block port 443) while still serving HTTPS on that port.
The full story
This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.
