[Mike]

Don't lower your ZA setting to Medium as you reduce the protection.
Setting ZA to Medium is a work around ,not a solution.
Uninstall KB951748 from add/remove.
You'll need to check the 'show updates' in ad/remove to access this.
MS ,ZA and others are working on a solution.

 

[Mike]

Now go get the ZA update for your version:
http://download.zonealarm.com/bin/free/pressReleases/2008/LossOfInternetAccessIssue.html

And you can reinstall the KB951748.

 

[Mike]

Pete ,XP has a 'system restore' feature.
Go to Start ,Programs ,Accessories,System Tools,System Restore.
I'm set for Classic view ,your's may be different.
Anyway ,prior to getting updates for ANYTHING on your 'puter ,set a restore point.
Anything goes nuts/away/crashes ,restore to set point you created.
I do this for all/any updates/upgrades/software installs -ANYTHING.
After resetting to the restore set point ,you can go online to find out what went wrong.
It was minutes after the KB951748 release that the microsoft forum and ZA forums were on the case.