Which is the best Free Anti Virus?

The first thing that comes to your mind when thinking of PC security is an Anti Virus. There are quite a few free anti virus available, the most popular being Avast, AVG and Avira. Before installing any, just have a look at the test reports on the page http://www.av-comparatives.org/comparativesreviews/main-tests

Avast and Avira perform almost equally, but I'll say that Avast has an upper edge because of its Boots Scan capability. Also Avira free version doesn't have rootkit protection but avast free version has :) AVG is not recommended, too many false positives.

A unique feature in AVG is its Link Scanner, but its not much effective. Use Web Of Trust as an Add-On for your Browser (which I recommend to be Firefox) instead.

We also have the less popular NOD32 and BitDefender. The problem with these is that they are too slow at scanning and are not updated as regularly. In terms of updates, again its Avast which gets the pie. It updates every 4 hours!

I personally use Avast! have been using it along with SpyBot, Zone Alarm and Spyware Blaster for two years now and without any infection.
Also all these are very compatible with each other, so no crashes.

Safe Computing!