Those aren't viruses. Your scanner is blocking potentially harmful webpages you're going to. Either stop going to websites that are questionable, turn OFF malicious website blocking in Avast (Recommended. Malwarebytes has better filters for this. Use the one if Malwarebytes, not Avast.) or if it's a particular couple of sites that always trigger it and you know they are not harmful, add them as exclusions in Avast.