Hi,
It is recommended to install all the Symantec features AV / PTP/ NTP with latest definitions.Always make sure that your computers are receiving definitions regularly.
You can upgrade your product to latest built i.e RU6 MP3
You windows machines should have all the latest windows updates /Patches.
Apply application and device control policies, block USB etc.
Disable Autorun.
Please follow best practice guide to handle virus issue.
http://www.symantec.com/business/support/index?page=content&id=TECH105236