Before Avast, I was using a lot of antiviruses...
The first antivirus I try on my PC was Norton. The antivirus was cool, but I when I run the scan option or full scan it slowdown my PC for 30-40%. After that I have decide to try the Kaspersky. This was definitely one of the best antiviruses that I have used, but because I have the pirate version, sooner they put me on the black list. The same story was with NODE 32.
Now I am using Avast for almost 2 years. The antivirus is free and it only keeps me save from antiviruses. I am not same hacker or IT developer, I use my PC so I can do my job, reading something in free time and gaming.
Here is the answer on the question: Why Avast is free?
''First, we do it because it is the right thing to do. Internet users need to be protected while they use the internet. A number of studies show that large numbers of internet users are still not protected while they use the internet—either they have no security product or the product they have has expired and they have not renewed it. So, Eda and Pavel (our founders) had decided years ago to make our core antivirus product free to home users. This is something we believe in and are committed to.''