This has just happened to me for the first time ever.
I do notice that my computer is telling me it needs to apply updates, it didn't give that indication to me yesterday. (so not sure if that's the issue or not)
After work (on my gaming computer at moment, which doubles as my work computer when I'm forced to work from my home study (as opposed to my home office)) I will apply updates and see if that makes a difference ... I also have my computer set up as never log out from Carl's site (some things are just TOO important to close down) and get that same screen that sdhoey showed. Oh yeah, it is currently Google Chrome browser with the duck duck go search engine. I just tried opening the Carl's site with Firefox, without a trouble. But on that one, I just clicked on a 'most visited sites' icon, and not typed it into the search bar as I had to with Google Chrome, tried typing it into firefox with duck duck go search engine, no captcha screen.