What happens if you blow off Microsoft's advice to disable antivirus applications before upgrading Windows XP to SP3? If you're lucky - nothing. If you're not lucky, you might not be able to finish the installation, or if it finished, you might have a system with an empty Device Manager listing and/or an empty Network Connections listing.
Hey, What Happened?
According to KB953979, this happens when the Fixccs.exe process, which creates and then cleans up temporary registry keys during the upgrade, can't remove some registry keys because an antivirus program says, "U can't touch this". The entries aren't actually missing from Device Manager and Network Connections - but if you can't see them, you can't touch them, either.
Many reports fingered Norton Antivirus as the cause, but it can happen with other antivirus programs if they're running during the upgrade process.
Hey, How Do I Fix This?
Microsoft provides a downloadable hotfix at KB953979, or you can click here and get it immediately. The hotfix is only for XP SP3.