Hi,
Best FREE Programs i would recommend is:
Avast Free Anti-Virus or AVG Anti-Virus Free Edition 2011, both good but i use Avast. Setup schedule to run the scan daily or weekly.
Malwarebytes Anti Malware (keep this software alongside a anti-virus software, one of the two above, requires manual update and scan)
Optional FREE software to keep your PC/Laptop running smoothly and tune-up and maintain the computer system performance, Install ccleaner or Advanced SystemCare Free
techs2010