Hi,
I would suggest to scan the system with Symantec power eraser to detect threat and remove them
http://www.symantec.com/theme.jsp?themeid=spe-user-guide
It might be your assumption only 1 file is suspicious but there can be multiple
You should run the Symhelp tool to find out suspicious files available on the System.
Symantec Help (SymHelp): http://www.symantec.com/docs/TECH170752
Submit all those suspicious files to the Symnatec at the following id
https://submit.symantec.com/essential
You would receive tracking id, you can PM me the tracking id.
Update the system with latest windows patches & Service pack, update all third party application.
Make sure all the SEP features are installed & having most current definitions. (Virus & Spyware /PTP/NTP)
Always follow the best practice: http://www.symantec.com/docs/TECH122466