Microsoft introduced an antivirus protection product FREE for home PC users. http://www.microsoft.com/security_essentials/
To qualify, you have to be using Genuine Copies of Windows Operating Systems (XP SP2 and SP3, Vista SP1 and SP2, and Windows 7).
Installation is simple too. Just four clicks and installation completes.
First click, Next to proceed on from Welcome Screen.
Second click is to Accept the license agreement.
Third click is to validate your copy of Microsoft Windows.
Fourth click is to begin installation.
Installation in progress…
And we are done!!!
This is how it looks.
You might want to change the default settings to suit your needs, else leave it as default will be good.