If your use is for Home, Non-commercial purposes then you would qualify for the free home and I think the explanation on this page covers the bases,
http://www.avast.com/eng/avast_4_home.html, see image.
So if your blog is a hobby, pastime, etc. and not a commercial enterprise you should be OK. If it is commercial, non-profit or otherwise you would need the Pro version. You could confirm your status with sales @ avast.com without the spaces.
You could download and use the Pro trial version for 60 days unrestricted access in the mean time, so no worries about 24 hours to receive a key (usually much quicker). When you know your status if you are eligible for the home version, complete the
avast! 4 Home Registration form and you will receive an email from register @ avast.com (without the spaces) with your registration key. Enter your registration key whilst on-line and the version will be converted to the home version.
Insert Registration Key - VideoSome might suggest it would be better to download the Home version, uninstall the Pro trial, reboot, install the Home version and enter your registration key.
If you don't qualify for the Home version you would have to purchase a Pro license and enter that key into the Pro trial version.
NAV can also be a bit of a pig to remove completely.
A link worth looking at, which is a program removal tool that can remove the remnants of a number of different Norton Programs:
Removing your Norton program using SymNRT