What is it?
Norton AV - navshext.dll
What does it do?
This file is a part of Norton AV. There is a common error while trying to uninstall Norton where this file fails to be removed. Their support page on this matter can be found here. You'll see a message that says: "Cannot delete navshext.dll. The specified file is being used by Windows." This happens even if the computer has been restarted in a clean boot or in Safe mode. The best fix is to unregister this .dll file and then delete the folder.
You'll want to keep an eye on this google search for any known viruses. The normal location of this file is C:Program FilesNorton AntiVirusNavShExt.dll