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.
You windows machines should have all the latest windows updates /Patches.
Disable Autorun.
Please follow best practice guide to handle virus issue.
http://www.symantec.com/business/support/index?page=content&id=TECH105236