What free anti-virus are you using? We installed AVG which looked good for protecting our home computer. But the problem is when we run the browser, AVG updates itself automatically even if the setting of update is in manual. With Chrome, it only automatically updates itself when we run Firefox. And to bypass the update we are using Chrome more often.
While installing Windows to my Laptop, the mechanic had installed the SmadAV antivirus which is still I'm using on my PC. I have found it much helpful & might help you, too.
It's free & for every PC OS.
To download it, Please visit softquack site for latest version.
I used to use Avast anti-virus back when I used a Windows System, now days though I'm on a Mac so I stick to apps from safe sources and use the protections that Apple Provides me with. If I'm suspicious about a file I generally won't open it or I'll scan with VirusTotal (a site that checks the file across multiple AV engines).