Hello,
The unmanaged clients can get definitions from internet, if enabled.
Incase if this is only 1 or few unmanaged client machines, then you could update these clients Manually by Downloading and Running the Intelligent updater which would update the Definitions.
Check this Article:
How to update definitions for Symantec Endpoint Protection using the Intelligent Updater
http://www.symantec.com/docs/TECH102606
The below articles tell you how to do this:
Using Intelligent Updater files to update client virus and security risk definitions
http://www.symantec.com/docs/HOWTO80903
How to manually update definitions for a managed Symantec Endpoint Protection Client using the .jdb file
http://www.symantec.com/docs/TECH104363
The above article will need to be used with this article (http://www.symantec.com/docs/TECH105498) to get the unmanaged client to allow 3rd party content distribution.
However, incase if you are carrying a Number of Unmanaged clients, then you may need to take assistance of Liveupdate Administrator Utility.
Check these Articles below to update:
Is it Supported to Configure Unmanaged Symantec Endpoint Protection Clients to Update from LiveUpdate Administrator 2.x rather than the Symantec Endpoint Protection Manager?
http://www.symantec.com/docs/TECH123388
Installation and configuration of LUA
https://www-secure.symantec.com/connect/articles/i...
Updating downloads in an internal LiveUpdate Administrator 2.x Server using the downloads from an external LiveUpdate Server
http://www.symantec.com/docs/TECH106254
How to change the LiveUpdate source of an unmanaged Windows Symantec Endpoint Protection 12.1 Client
http://www.symantec.com/docs/TECH166129
Hope that helps!!