The choice of programs: Antivir, Avast and AVG are the most used and most well known freeware antivirus programs, and I use or have used all three for long periods of time.They are also most likely the top three best freeware antivirus programs.Not only are these on par with the best commercial program, Antivir in fact has the best detection of any program free or paid according to AV-comparatives.org’s numbers.
The programs tested were subjected to 1,274,928 instances of malicious code collected between Apr 04-Apr 08.
The reason: any malware collected prior to this is considered fairly well known by now* Note: no free version of these offered. The data seems to show that overall the detection rates are very similar (the differences are unlikely to be meaningful), with the exception of AVG which has a somewhat lower rate of detection than the others.2.
The programs tested were subjected to 45,831 “new” instances of malicious code collected between Aug 4th-31st 2008 (4 weeks in total).
The results above seem to show that when handling yet unknown threats (malicious code that is so brand new that it has not been added to the program’s database), Antivir and Kaspersky have an advantage over the others.3.
However, AVG scores another strike against it in terms of its scanning speed, which is significantly slower than the other two.
The freeware version of Antivir displays an advertisement on every update, which is rather undesirable; however, this can be easily disabled (look here, here, or here).
Versions tested: note that the versions tested were the paid versions.
I am assuming that the basic engine is the same in the free version as well, and that the results apply there.
It also “does not support email scanning”; however, this is also a non-issue in my opinion, a red-herring designed to scare less tech-savvy users into purchasing the paid version.
The reason I say this is a non-issue is because although Antivir may not scan your email for virus as it downloads, it will still protect you from it afterwards, not just during normal scans as it will also intercept it once it is on-disk and/or if and when it tries to act up.
But if you use multiple platforms, you're better off with a cross-platform suite like Trend Micro Maximum Security.