Norton will not resolve Malware

Hello, forgive me if I have posted this in the wrong place.  I am a happy Norton user - with many years of virus free computing. However recently my PC  contracted malware problem. My email account keeps sending out emails to addresses that I have used preciously.  Try as I might to clean my PC .... they keep getting sent out.     Below is an example:

Subject: Fw: new message

Hey!

New message, please read http :// legacy life club . com / greater . php

.................................................................................................................

Any ideas how I can stop it once and for all?

Thanks

Viv