Each antivirus, internet security, etc are not able to do the job alone.
For me, i use Panda Internet Security 2016 and Superantispyware Pro, both are paid version.
Panda is active, whereas
Superantispyware is not active.
Panda check for suspicious websites may able to visit your computer.
Superantispyware is mainly lookout for temp files, cookies, etc that store spyware, malwares, virus, etc.
Superantispyware is not active, but do daily update virus /malware files that is detected worldwide.
Hence both will not interfere with each other.
Windows do have its own antivirus loaded, mostly in the background.
I recommend you can go to
SUPERAntiSpyware free version, and download & do full scan.
The malware, virus, spyware, etc files are listed, before you press Continue to remove.
You can continue to use this either run daily or few days at a time, just do quick scan will do.
Being doing this for several years, without any issue. Just need to update the database, before run.
My friend computer had over 200+ virus/malware/spyware, after the full scan i did for him.