Please follow the following steps :
1. Install all the 3 components of SEP ( AV and AVS, NTP and PTP)
2. Always update the virus definition Virus definitions and IPS signatures
3. Use the lowest privileged user possible:
4. Disconnect Mapped Drives:
5. Disable autorun functionality:
6. Patch your OS with latest security Updates
7. Password protect any shared folders, close open shares and enforce the use of strong passwords:
The 5 Steps of Virus Troubleshooting
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2007011014341948
Security Best Practice Recommendations from Symantec
http://service1.symantec.com/SUPPORT/ent-security.nsf/docid/2009010808340848