Poweliks!gm keeps coming back!

I am running Windows 7 which is up to date. I have Norton 360, also up to date and recently installed MalwareBytes, also up to date. Malwarebytes finds nothing. After it initially cleaned the system of what I think were unrelated issues, it has run clean. Here is the issue.

Norton 360 will find poweliks!gm, remove it after a reboot; the next scan will be clean. After a short time the next scan shows another instance of poweliks!gm usually in one or more .tmp files in syswow64 along with entries in the registry. Since installing MalwareBytes it is blocking outbound attempts, usually two, to a couple of WEB sites by dllhost, I'm assuming this is poweliks!gm. I've run Norton power eraser. It finds some files but all are "unknown" and don't appear to represent a clear threat.

Now, after the last reboot and cleanse Norton is telling me it is processing Trojan.poweliks!gm yet again. How do I get rid of this for good?