Hello,
What version of SEP are you running?
In case of SEP 11.x, check this Thread with similar Query -
https://www-secure.symantec.com/connect/forums/sep-and-vdi-considerations
In case of SEP 12.1, Check these Articles:
Symantec Endpoint Protection 12.1 - Virtualization Best Practices
http://www.symantec.com/docs/TECH173650
Does Symantec Endpoint Protection 12.1 support VMWare vShield?
http://www.symantec.com/docs/TECH175568
Using Symantec Endpoint Protection in non-persistent virtual desktop infrastructures
http://www.symantec.com/docs/HOWTO81133
Symantec Endpoint Protection 12.1 & Virtualization
http://www.symantec.com/docs/TECH194383
Secondly, In case if these machines are cloned, then there are few steps you may need to follow -
How to prepare a Symantec Endpoint Protection 12.1 client for cloning
http://www.symantec.com/docs/HOWTO54706
How to repair duplicate IDs on cloned Symantec Endpoint Protection 12.1 clients
http://www.symantec.com/docs/TECH163349
Hope that helps!!!