Avast antivirus is my secondary choice to AVG antivirus. These two antivirus software include free versions. I load Avast antivirus whenever I cannot install AVG antivirus on a computer.
One distinction between these two pieces of software is their free licensing. AVG is free for an eternity as of this blog post creation. Avast requires that you accept either a twenty or thirty day free trial.
However, if you register with Avast antivirus you can register in one year increments. Once you have Avast free antivirus successfully installed, right click on its system tray icon. Select "Registration Information" and a "Your Subscription" window will open.
You want to click on "Register now". Choose "Standard protection" on left hand side. This choice is for free version of Avast.
Avast requires registration to obtain a one year license of their free version. A "Register my FREE 1 Year license" window opens. You will need to enter in an email address and click on "Register".
You are now registered to use Avast antivirus free edition for one calendar year. Avast claims you can re-register in one year increments for as long as you like. Another point of contention is that if you register Avast for only twenty or thirty days then you will need to remove and reinstall that software to possibly use it again.
However, windows based programs don't clean themselves up very well and it is possible you could have old registry entries that would not allow you to use Avast antivirus. You might be able to cleanup your computer with an application similar to Ccleaner. It would make sense to just go ahead and register now so that you can save possibly avoid wasting time later.