I thought I would post this as an aid to those (including myself) who are experiencing this problem. In the most severe cases where NIS10 always fails to load and the PC is not behind a hardware firewall and ISP AV filtering, the PC can be left totally exposed to hacking and malware.
I was surprised that Symantec has not offered a quick temporary fix given the scale of the problem and that XP continues to be the largest installed OS base.
Here is what I did to get back up running on four XP systems and maintain some semblance of current security:
(1) I disconnected each system from the Internet. The easiest way to do this is simply unplug your network cable if you have one. I am not sure about WIFI users (probably just temporarily disable it in the BIOS).
(2) I restored image backups of my system disk which were still running NIS10 17.1.0.19. (If you don't have an image backup, then you need to uninstall NIS10 and find out from Symantec where you can get a direct download link to NIS10 17.1.0.19. Of course, do this before you take yourself off the Internet.) If someone knows a link for this, then please post.
(3) Reboot and go into NIS10 Computer Settings and turn off Automatic Live Update. This will prevent the 17.5.0.127 patch from getting pulled down again.
(4) Reconnect to the Internet.
(5) Daily download the security defs from Symantec and run the executable which will update NIS10. This will keep you up to date while avoiding 17.5.0.127. Here is the link (use the first updater):
http://www.symantec.com/business/security_response/definitions/download/detail.jsp?gid=n95
I hope that will help some of you until Symantec addresses this. Personally, I don't understand why patching and streaming security updates cannot be two separate options in NIS. Also, I don't understand why Symantec has not made NIS10 17.1.0.19 available for download/reinstallation while at the same time pulling the 17.5.0.127 patch until a new and working patch can be provided.
I hope this helps.