I can't take the credit for this fix. I did find this solution on the Apple discussion board. It looks like a promising solution though:
To stop the pop-up, Go to System Preferences: Security. Check the box next to "Require password to unlock each secure system preference." Then lock Security.
Try this cure for Security update...
[http://discussions.apple.com/thread.jspa?threadID=1730909&tstart=0]
The locations are actually...
/Library/Preferences/SystemConfiguration/preferences.plist
/Library/Preferences/SystemConfiguration/com.apple.airport.preferences.plist
/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist
/Library/Preferences/SystemConfiguration/com.apple.nat.plist