Run the Threat Analysis Scan:
How to run the Threat Analysis Scan in Symantec Help (SymHelp)
http://www.symantec.com/docs/TECH215519
Also check these additional links:
Is your system infected? Symantec tools to help clear an infection
https://www-secure.symantec.com/connect/forums/your-system-infected-symantec-tools-help-clear-infection
Symantec Endpoint Protection – Best Practices
http://www.symantec.com/page.jsp?id=stopping_malware
Security Response recommendations for Symantec Endpoint Protection 12.1 settings
http://www.symantec.com/docs/TECH173752