I recommend using AVG Free for antivirus and running Malwarebytes once a month or whenever you suspect malware may be present on your computer. This is the advice I give to all my clients. As for me, I use a Linux OS called Ubuntu. No virus protection is necessary for any Linux OS, which also increases your computer's performance because to Antivirus software is running in the background. Linux OSs are free.
I am very frustrated in the amount of Malware and Browser Add-ons that get through the AVAST Firewall and can not be cleaned by the Premier version of Avast.
Some of these problems have leaked through even when the source of my downloads is what I believe is a secured site like CNET.
There should be a law penalizing companies that distribute sofware and attach all kinds of junk that ruins the performance of your computer. They should all be in jail for adding to programs unwanted add ons, specialy those you can't uninstall by normal means of uninstallyng.

Chowhound
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