There is a link which bring you to download site -Rapidshare.There you can chose an option to download:Free or premium user.
I think this avast version is a profesional which mean you have to pay after a trial period.But inside of this post you have options to make it free for you.Download and you will see how.
But you have also very good free antivirus software which are
-Avira antivirus personal--My favorite
-Avast personal and
-AVG personal
Just google for and you will find them.