On Nov 8, Norton blocked an intrusion by "Trojan.Powerliks!gm" , but my computer immediately slowed down and the Task Mgr showed an unusual amount of activity with the "DllHost.exe". Subsequent research suggested that there was an infected thumbnail. I disabled thumbnails and the computer returned to normal. When I enable thumbnails, the intrusion is again blocked and the computer slows down again - disable thumbnails and all returns to normal. How do I find the infected thumbnail?