I just recently rebooted my Windows XP after downloading the latest patches via the built-in automatic Windows Update Service when I suddenly noticed that I could not get any internet connection via Firefox any longer. Ping and tracert worked, though.

After trying different things I finally came to the conclusion that shutting down ZoneAlarm made everything work perfectly again.

After searching the internet for this issue, I found a nice article on heise online, saying that it has to do with the recent Windows DNS patch.

In the ZoneAlarm forum, the support suggests to deinstall the patch MS update KB951748, which does not seem to be the best solution since the patch solves a big security issue. Others suggest that lowering the Firewall and the Trusted Zone bar to “medium” will make ZoneAlarm work again.

I for one have deinstalled ZoneAlarm and activated the built-in Windows Firewall. I will rather wait for a proper ZoneAlarm update - or maybe I will find out that my router firewall plus the built-in Windows Firewall is more than enough security.

You are welcome to share your thoughts on this subject.

[Update from 2008-07-10]
As of today, CheckPoint provide a fixed version of their Firewall ZoneAlarm (see this announcement in the forum which replaces the suggestion to deinstall the patch which was formerly provided in the forum - the latter has been deleted).