Antivirus programs:
AVG anti-virus - A free and effective anti-virus program - More info at Grisoft.com
Avast anti-virus - Another good choice in freeware anti-virus protection. More info at: Avast.com
Anti-Spyware programs:
Microsoft Defender (formerly known as Microsoft Anti-Spyware)
Spybot Search and Destroy - Free anti spyware program. More info at support available at: Spybot home page.
Ad-Aware SE - Simple to use Anti-spyware program. More information and support at: Lavasoft home page
You may use more than one anti-spyware program to keep your computer safe, but it's usually not a good idea to use more than one antivirus program - if you have an anti-virus program on your computer already, be sure to uninstall it before you install a new one.