Windows Firewall options are grayed out in XP SP2

Problem:

When you open the Windows Firewall in the Control Panel or you launch the applet thru RUN box (firewall.cpl), a message at the top reads "For your security, some settings are controlled by Group Policy".
You can't change your firewall settings at this point.

Solution:

You have to reset the firewall settings by deleting the Windows Firewall registry.

1. Open Registry Editor by typing Regedit in the RUN box.

2. Navigate to this location:
HKEY_LOCAL_MACHINE \ SOFTWARE \ Policies \ Microsoft \ WindowsFirewall

3. Backup WindowsFirewall key:
a. Right-click on it, choose Export.
b. Export Registry File box will appear.
c. Enter any label for this registry in the File name bar.
d. Then click Save.

4. Delete WindowsFirewall key.

5. Restart your computer.

What went wrong?

A virus might disable the Windows Firewall settings so you have to run a full system scan immediately.