You can find all information regarding SecureDNS here:
How to for configuring OS or Router to use Comodo SecureDNS, how to switch back to your previous DNS Servers if you selected it and wish to stop using it. FAQ’s and other information related to this service.
Vista/Win7 Instructions
XP Instructions
Mac OS X
Router
How do I stop using Secure DNS
CIS Help file entries (extended versions)
Windows XP enable/disable SecureDNS
Windows Vista/Win7 enable/disable Secure DNS