To keep your PC from online or Virus threats you need a strong Anti Virus software.
These are the "Top 10" Anti virus software.

1. avast! Anti Virus 2008

2. Norton AntiVirus 2008

3. Kaspersky Anti-Virus Personal

4. BitDefender Antivirus Plus

5. McAfee VirusScan Plus

6. F-Secure Anti Virus

7. F-PROT Antivirus

8. G Data AntiVirusKit (AVK)

9. AVG Anti-Malware

10.Eset Nod32