I don't think that it's been compromised, as I run SSH on a non-standard port, have a hardened login process including disabling root login, and use random strings for passwords. Have there been any recent exploits?
However, I will be careful, and have taken it offline. I just checked processes for any other sshd's running, and there is just the one. Or is it likely it's been "hidden" or something?
I did a quick check of files on the server, and there doesn't seem to be anything suspicious.
Also, I tried connecting to SSH on the same port as the webserver, and nothing is showing up.
One thing though: I switched my router to pfSense a while back, and when configuring the firewall rules, I accidentally set up all connections to forward to all the ports. Could this have caused the problem?
Edit: I just tried connecting to the server through my LAN, and I'm still getting the message, so it's not pfSense's fault. You're probably right about it being compromised. I will do an OS reinstall. Are there any special precautions I should take for the reinstall?
Edit 2: I had pfSense applying that port forwarding rule to connections from the LAN as well, so it may be its fault after all. I'm rebooting the machine right now to see if I can kill that rogue SSHd if it's really there.
Edit 3: Disregard the stuff about pfSense. I wasn't looking at the right configuration page. I guess the firewall rules were set up correctly, but I just didn't know how to read them. I originally went to the port forwarding page and set up everything through there, and pfSense automatically set up firewall rules from that.
On another note, I just stopped SSH on my server, and then attempted to access the CGI again, and I'm still getting the string. Is there some way to find where this other SSH thing is running?
Final edit: PEBKAC 
I'm developing some web software, and there was a mistake in my configure command that was causing this issue. Sorry for all the trouble :/
Thanks!