Hello,
I am not sure if you are talking about Backdoor.Ploutus which has been added to the definitions on 09/04/13.
http://www.symantec.com/security_response/definitions/rapidrelease/detail.jsp?relid=2013-09-04
Every Antivirus company has its own naming conventions.
The best way to understand if Symantec Endpoint Protection is detecting this Threat or not is by submiting the files to the Symantec Security Response Team.
How to collect and submit to Symantec Security Response suspicious files found by the SymHelp utility
http://www.symantec.com/docs/TECH203027
Secondly, check these Articles:
Naming convention for statically named virus definition update files
http://www.symantec.com/docs/TECH161663
Virus Naming Conventions
http://www.symantec.com/security_response/virusnaming.jsp
Hope that helps!!!