Links to Free System Security Software

MalwareBytes Malware Bytes Anti-Malware searches for spyware programs and removes most of them from your computer. 98% of home computers have spyware.
SpyBot Search & Destroy Spybot Search & Destroy searches for spyware programs and remoes them from your computer. This can be used in conjunction with Malware Bytes.
AVG Free AVG Anti-Virus Software scans and removes viruses from your computer
Trend Micro House Call Trend Micro House call is an online virus scanner
Windows Update Windows Update installs important security patches for various vulnerabilities found in Microsoft Windows