Hello,
In your case, it is advisable to follow few important steps:
1) Make sure all these machines are Patched with ALL Latest MS security patches and service packs.
2) Make sure the machines are installed with the Latest Symantec virus definitions.
3) Disable the Autorun Feature on the machine.
Preventing a virus from using the AutoRun feature to spread itself
http://www.symantec.com/business/support/index?page=content&id=TECH104447
Later, incase of suspicious activity still happening, then follow the steps provided in the Article below:
Using Symantec Support Tool, how do we Collect the Suspicious Files and Submit the same to Symantec Security Response Team.
Check the below articles on handling infections.
Best practices for troubleshooting viruses on a network
http://www.symantec.com/docs/TECH122466
Security Best Practice Recommendations
http://www.symantec.com/docs/TECH91705
How to Use the Web Submission Process to Submit Suspicious Files
http://www.symantec.com/docs/TECH102419
Security Response recommendations for Symantec Endpoint Protection settings
http://www.symantec.com/docs/TECH122943
Hope that helps!!