Ok, I think I've figured out what happened.
My main hard drive failed and a few days ago I restored from a backup that was taken shortly before re-joining Aquiss. I imagine you can tell what follows...
The primary and secondary DNS were not accessible and so the OS failed-over to Open DNS servers.
The only thing that made me think the ISP had anything to do with it was the message at the top of the redirected page:
"This search brought to you by www.aquiss.net and OpenDNS, teaming up to provide you with a faster and safer Internet experience."
I'm sure everything will be back to normal when I re-apply the correct DNS addresses. Sorry guys, false alarm!