help trojan keeps redownloading itself!

ok i just posted this then norton said i didnt have permission to view my own thread ugh really norton? this trojan keeps installing itself AFTEr being uninstalled by norton it turns off auto protect and downloads itself luckily norton detected it again and uninstalled it but i want to get rid of it for good!

Filename: precomp.exe
Threat name: Trojan.Gen.SMHFull Path: c:\users\zach\appdata\local\temp\is-0n3nm.tmp\precomp.exe