I installed Windows 10, noticed that NIS had disappeared. I downloaded and ran the Windows10NortonUpgrader. It looked like it was installed, but it wouldn't start. Next I downloaded and ran the remove and reinstall tool (NRnR). Still wouldn't start. I downloaded the Remove Norton tool and removed NIS. Then downloaded a new NIS and installed. Still wouldn't start. I let the laptop rest a while and then ran the downloaded install again. FINALLY, it worked! Whew.
I did all this on my "extra" PC. I think I'll wait a few months before I install Windows 10 on my main computer -- maybe Norton will have the kinks worked out by then.