How do I permanently remove Trojan.Zefarch?

Every time I start up my computer, Symantec Endpoint Protection comes up and shows the results of an Auto-Protect scan. It always comes up with two files named overlay.xul and the risk being Trojan.Zefarch. Norton says they are deleted every time, but when I start up my computer again, it shows the same message. However, I cannot manually delete Trojan.Zefarch because it does not show up in my Task Manager processes and it does not show up in my Registry Editor.