Microsoft Security Essentials is one of the best antivirus and antimalware product which is available absolutely free to use.
Its a product from Microsoft and can be installed in genuine Windows OS. Microsoft Security Essentials provides real-time protection for your PC that guards against viruses, spyware, and other malicious software.
Download Microsoft Security essentials v4.10.0219
For windows xp, vista and 7, 32bit - 12 MB: Download