I think my Mac has a Java Script Trojan virus and I don't know what to do!

Okay, so I was browsing Yahoo on my MacBook Air and I noticed something up in the search box that read "Safe Finder." I looked it and found out it was a virus, meaning my Mac may be infected!

I visited an site called PCRisk.com (image below) and it recommended I download a free version of a software called Combo Cleaner to get rid of the Safe Finder virus.

So I downloaded a free version of Combo Cleaner and after scanning, it came up with this:

It says I have to buy and download a Premium version to get rid of these infections. To make sure I would be getting my money's worth, I looked up Combo Cleaner and found some reviewers calling it a scam. Now I'm not sure what to do and I'm getting really scared!

From what I could gather, the Trojan is in a file called Inject.js. I think this means it's infected Java Script. How do I get rid of it? Should I download Combo Cleaner?