In the grand scheme of things, it's not the evilest thing to have ever happened. At some point the Windows auto-updater decided to push a new feature that changes the network DNS settings to make them point to some Oracle DNS server. If you undo the changes without disabling the "feature" in the app, it'll reset them for you. It was done with the claim of speeding up DNS lookup or somesuch.

It's a checkbox, and no doubt it would remember the setting if I changed it, but the idea an app would change my DNS settings (which, in my case broke an internal app that was admittedly fragile to begin with) without my permission was enough for me to cancel my DynDNS account there and then while I cobbled together a replacement.

I recently quit DynDNS after many years of use because of sheer frustration. I dropped my paid subscription because their Mac OSX updater hasn't been working correctly for years. It would forget its settings and/or fail to update. I filed a bug report with DynDNS and spoke to their tech support, and it never got solved. (I suppose I could have found a third party updater, but I expected their own updater to work.)

Hurricane Electric does free DNS hosting and supports dynamic DNS

Since they stopped offering a free plan, I imagine. I just paid them the money, it's worth it.

There are better free alternatives like freedns.afraid.com out there if you dont really need to rely on your router that may only support Dyn.com