These files are all free, however, use them at your own risk!

AVG Free Edition - Free anti-virus software

Windows Defender - A free Microsoft product that fights spyware

Spybot Search & Destroy - Fights spyware

Spyware Blaster - Blocks Spyware from your computer

Having only 1 Anti-Virus Program is fine, if you have more than 1 they may conflict with each other. Anti-spyware Programs are different, the more, the merrier. So download and install all 3.