Firewall and System program

I have Norton Security System 2011, Windows XP

 

Is there a legitimate program named SYSTEM that would need access through the firewall? There is no info displayed on it like Path, or Publisher, or Digital signature. The info I got from the log file was Traffic Description: Outbound UDP, Port 138.

 

Is this a core system file, or a trojan masking as a system fie?

 

Also is there a guide somewhere how to configure the firewall for maximum security (meaning deny rather than allow) other than the setting Block All Network Traffic?

 

Thanks