Many users of the ZoneAlarm firewall have been floored by a fix to the net's addressing system.
Those hit found they could not get online after installing a Microsoft patch to close a security loophole.
On Tuesday Microsoft released its patch for DNS as part of its regular security update cycle.
However, many found that as soon as they applied the patch, known as KB951748, they could no longer go online.
The problems only affected those with machines running Windows XP or 2000.
http://news.bbc.co.uk/2/hi/technology/7499260.stm