Avira actually keep changing their tactics. I had been using Avira for a long time until a few days before, and there were no advertisement popups being displayed. However, a few months before, there were advertisement popups. So, maybe they have started to show them again.
Avira worked fine on my system for quite many months. A few days ago though, it caused network problem for me, because of which I was not able to connect to the internet. It was uninstalled, and the network was back again. It was strange though, because I never faced any such problem with it before. Anyways, I am back to using Avast, which is surprisingly working quite well and light on my current P-III system.
I agree with wdhpr, that although AVG works well for some, but I found it heavy on my system.