It protects you in real-time by analyzing unknown files before they get to you. So relax: With Avast, you're running the most trusted antivirus out there. Download Avast Free Antivirus and run the setup file as an administrator. When the Avast Setup wizard appears, click Install for default installation or Customize. Update files can also be downloaded from these pages if required e.g. if your computer does not have an Internet connection. Updates are usually released on a.