The definition are updated on a daily basis...
Its free for non commercial purposes
download it from here
http://www.download.com/Avast-Home-E...=dl&tag=button

couple it with Comodo Firewall (again a freeware) and Spybot Search and Destroy (yes its free too) and you have a deadly combo that keeps your PC as safe as The norton internet security if not safer and at no cost......