That is not an infected OS.
Is that an infected search engine?
Well no, that's not an attack, it's just that the search engine has indexed a URL using the IP address instead of the domain name. If you click that link, then on the error page change https to http, it'll redirect you to the real forum.
But, without knowing the domain name, the browser can't tell if it's legit or not.
It's actually an error on the forum's part, I think. If you access the IP address using http, it redirects you to the domain name. But using https, it doesn't. Not that the forum must do a redirect, but it's nice when possible.