Please open a thread on Antivirus forum. BTW this kind of problem is usually related to some malware trying to exploint your PC to send SPAM. If it is necessary, please open a case with TechSupport.
Try deleting your temporary Internet files, download the latest Rapid Release definitions, and run a full scan in Safe-mode.
If that fails to detect anything, try running the Power eraser or SERT tool if you have access to it.
PE - http://security.symantec.com/nbrt/npe.asp?lcid=1033&origin=default
SERT - http://www.symantec.com/business/support/index?page=content&id=TECH131732&locale=en_US