I followed the steps in the Symantec Security Response link - disable system restore/virus defintions up to date/run full system scan.
Scan came up clean again and still received the pop up image seen above. I used the link How to Find Suspected Threats on your computer and dowloaded Autorun. A careful review of all the files (with Microsoft and Windows entries viewed) exposed what I believe was the culprit - tgfm.klo. I deleted the file and restarted the machine, I'm waiting to see if the problem is solved.
I appreciate your help and advice!