Hi,
Did you scan with Symantec power eraser?
Symantec Power Eraser is the latest Symantec Recovery tool. The tool is aimed at the detection and clean-up of "zero-day" threats as well as other threats which may have infected the user’s system. Zero-day threats are those that take advantage of a newly discovered hole in a program or operating system before the developers have made a fix available – or before they are even aware that a hole exists.
Before submitting it to the Symantec go through the following steps
1) Install all the SEP features i.e. AV/AS, PTP & NTP.
1) System should be updated with Service packs and windows patches.
2) Make sure the machines are installed with the latest third party applications.
3) Disable the Autorun Feature if not using SEP 12.1.
4) Scan the full system in safe mode.
5) Use Symantec power eraser to scan the system.
http://www.symantec.com/theme.jsp?themeid=spe-user...
Best practices for responding to active threats on a network
http://www.symantec.com/docs/TECH122466
If these steps couldn't help then I would also suggest to submit suspicious files to the Symnatec.
How to Use the Web Submission Process to Submit Suspicious Files
http://www.symantec.com/docs/TECH102419