Quote from a website found in a brief search:
If you are operating behind a personal firewall, you will need to open the following ports to enable Symantec AntiVirus Corporate Edition client/server communications and LiveUpdate to work correctly:
TCP and UDP port 2967 - RTVScan
TCP ports 80 and 443 - LiveUpdate
UDP port 38293 - Intel PDS
For more information on port configuration, see Symantec Document ID 2005033011582148.
Open up port 443 for Windows Update.