After you install a version of Symantec Endpoint Protection earlier than 12.1.6, Windows computers sometimes hang on startup. This issue is intermittent, and may not occur every time the computer is started.
The Symantec Endpoint Protection Auto-Protect component does not properly release its opportunistic lock (oplock) on the VIRSCAN7.DAT file. The default location for this file is C:\ProgramData\Symantec\Symantec Endpoint Protection\12.1.4112.4156.105\Data\Definitions\VirusDefs\20150114.001\VIRSCAN7.DAT.
This issue is fixed in Symantec Endpoint Protection 12.1 Release Update 6 (12.1.6 or 12.1 RU6). For information on obtaining the latest build of Symantec Endpoint Protection, see Download the latest version of Symantec Endpoint Protection.
You can use one of the following workarounds until you can update to 12.1.6 or later: