Microsoft closed a DNS-related security loophole that has been known since March 2008. The flaw would have allowed malicious hackers to redirect users to fake websites, even if they typed the correct address.

Microsoft's patch was released on 2008-07-08 to automatic updates. But many or all users of Windows 2000 or XP and the popular ZoneAlarm firewall found that they could no longer go online after the patch was installed.

On 2008-07-09 CheckPoint released an update to ZoneAlarm, version 7.0.483, that solves the conflict.

If unobtainable, temporary solutions are to uninstall the KB951748 patch, to use System Restore to set the system back to a restore point before that patch was installed, or to temporarily lower the ZoneAlarm security setting to "medium".