Unable to access several sites and install apps in appstore. A possible malware issue. What do I do?

Hey guys,

I've been using an 8 GB Mac Mini with a 2.6 GHz i5 processor running the Mac Yosemite OS X 10.10.5 (14F27).

I haven't had any problems with this until I visited a torrent site (I hate visiting but unfortunately I did this one time). Ever since that unfortunate activity, I get mackeeper pop-ups and my default search engines on all my browsers like Safari, Firefox and chrome automatically changed to trovi. I'm unable to access 90% of the websites including YouTube except facebook, twitter, Netflix, gmail, google, yahoo and other mail clients. I get a "unable to connect" on firefox and "Safari can't connect to the server" error messages. I checked with the ISP and proxy settings but no issues there as my other apple devices like the ipad and iphone work fine on the same wifi network. I cleared all extensions, cookies and cache but no success.

I'm also unable to access the Appstore to install apps. I wanted to do a memory clean and a malware removal but couldn't that since the appstore couldn't contact the server.

I mainly use this machine for browsing and audio production through Logic Pro X.

Is it a malware issue? If yes, how do I combat that? Should I format my HD and upgrade to El Capitan? Will that solve the issue?

Kindly help.

Cheers,

AR