It appears that if you are running Windows XP Service Pack 3 and using ZoneAlarm firewall software, when you install patch KB951748 (MS08-037) that came out yesterday’s “patch Tuesday” bunch, it breaks ZoneAlarm. You cannot access the Internet until you either uninstall the patch or turn off ZoneAlarm. This patch is related to the DNS poisoning exploit that came out recently, so it should be applied. What to do? Well, one suggested workaround (other than the two mentioned above) was to lower the security settings to medium in ZoneAlarm. At least then you don’t have to disable it entirely. Another suggested fix has been to leave ZoneAlarm at High and set the Internet Security Zone to Custom and add the following rule “Allow outgoing TCP Ports:80,443”. I cannot verify that these fixes work, I don’t use ZoneAlarm myself, but others hit by this problem have had success with them.
Here is the Microsoft link with information about the patch:
Here is the official link from ZoneAlarm about the problem: