Windows XP patch screwed up Internet connectivity with ZoneAlarm

Just now, the Automatic Updates in my PC downloaded several patches for the Windows XP operating system, which require my confirmation to install them, and need to restart the PC after installation.

After the restart, I was unable to connect to the Internet anymore. I couldn't contact with the mail server and also couldn't browse the web. However, I found that I could still resolve domain names and perform the "ping" action. This mean the Internet line is still up and running, but somehow the outgoing TCP connections are blocked somewhere.

I disabled the ZoneAlarm firewall, and the Internet connection was back to normal. So, the problem is dealing with ZoneAlarm.

I enabled back the ZoneAlarm function, and looked into the log of ZoneAlarm firewall. Whenever I made an outgoing TCP connection, it is blocked by ZoneAlarm.

This problem is solved after I set the Internet zone security level in ZoneAlarm from High to Medium.

Then, I found out from ZoneAlarm User Forum that this problem is actually caused by the KB951748 Microsoft Update, which suppose to fix up the security flaws in Windows Domain Name System (DNS). This fix has changed some kernel file that ZoneAlarm is working with, therefore causing the problem.

If you are also having the same problem, you can try my workaround method as mentioned above, or you can try to uninstall the KB951748 security fix from the Windows Add/Remove Programs control panel.