Are you kidding? 
For free antivirus, doesn't avast! home edition offer you enough protection? for me avast! home with its fast and reliable update mechanism are more enough.
Alternatively, if you want the world-class-full-featued antivirus you can get eTrust EZ Antivirus from CA one year for free, over 95% of fortune 500 companies use CA software, shouldn't you? 
http://www.my-etrust.com/microsoft/
LOL. eTrust EZ Antiviurs has an awful user interface and performed very lack luster when I tried it. Also it never ranks well by independent reviews found at sites such as pcmag.com, pcworld.com, cnet.com and etc.
When I last used it, it was only compatible with IE and not Firefox which is terrible because no one should be using IE as their default browser when you compare the two together. If you combine avast! which supports both Firefox and Opera you have a much more secure environment. Neither Firefox nor Opera use Active X controls or BHOs. Did you know that other big name antivirus companies such as McAfee and Norton only provide full support for an outdated browser such as IE. avast! stepped up to the plate and is ahead of the "Big Money" companies by providing this support. Bigger doesn't mean better, especially when it comes to software. Norton and McAfee are much bigger than Computer Associates when it comes to revenue and worldwide use. However, I would use eTrust Antivirus over McAfee and Norton for several reasons but thank God for avast!, the cream of the crop.
Poll