I would never have known about this had I not read this article and the comments here, and have been running SSH servers for a very long time. The solution I'm

I would never have known about this had I not read this article and the comments here, and have been running SSH servers for a very long time. The solution I'm particularly fond of is mentioned in Daniel's blog comments, which is to use iptables to block externalip:22 and redirect a non-standard port to localhost:22.