My view on Free apps.... if they are free:
1\ Who ever writes them cannot have the resources to respond to the dozens of new viruses which are released on a daily basis -its too big\complex a problem even for a genius....
2\ If its not a 'proper commercial company' with a lot of Kudos, how do you know something you dont want isnt being embedded onto your system.
3\ Of all the companies I have used, almost 100 hundred small to medium networks - Norton (2011) is currently my preferred choice, and a vast improvement on the CPU hogging 2008-2010 versions.
You will find with companies like avast and zone alarm that they offer a basic version of their product, which is perfectly good, as a sprat in the hopes that you'll upgrade to the paid version. A bit like supermarket loss leaders.
As for Norton I wouldn't have it anywhere near any m/c I own because of the problems it's caused me in the past.