Consider the same strategy in step 2 for antivirus. Keep one antivirus solution installed on your computer (like Norton Security Scan / Norton Antivirus download in 1st Step)  but use other company’s free online virus scans and antivirus to supplement your computer's antivirus installed on your computer. Popular free online scan services will also significantly decrease your computers vulnerability to new virus threats.

• Trend Micro antivirus online - an effective and established free online virus, spyware, and antivirus, scanner
• Panda antivirus online - another great popular online antivirus scanner
• Free AVG Antivirus - if you havent downloaded Norton Antivirus or Spyware Doctor consider Free AVG. This will need to be installed on your computer. This software also has accurate scans.
• Free programming resources - another useful website that lists all of the free online anti virus and anti spyware scanners available.