With Microsoft Security Essentials freely available to anyone with a valid Windows license, I see no reason to ever pay for home-use A/V software. The only reason MSE doesn't come standard with Windows is because the other A/V vendors would sue Microsoft for antitrust violations. Also, OEM companies like Dell, HP, Acer, etc. receive kickbacks to bloat up your PC with pre-installed crapware like Norton.
Download link:
http://windows.microsoft.com/en-CA/w...ity-essentials