I love Microsoft Security Essentials. I love the integration, ease of updating, protection and the price! For an application as utilitarian as virus scanning, free is a great deal.
Microsoft claims the updated anti-malware engine makes the software faster and smarter at detecting security hazards. The software now also ties in with the Windows Firewall, giving you the option of turning the firewall on or off. The new version integrates with Internet Explorer to detect Web-based threats and can watch out for malware coming in through a network, though only for those running Windows Vista or Windows 7.
Businesses with up to 10 users can also install the product for free. Larger business need to invest in the Enterprise ForeFront.