Lost Weekend

I spent most of the weekend trying to delete a virus that showed up on my Friday night automatic scan. When I got home from baby-sitting on Saturday afternoon, I ran Norton Anti-virus and it said the Delete failed and directed me to their Web site for instructions. I was involved in this merry-go-round until bedtime and most of Sunday. The virus is "adware.gen" and it was on my external backup drive. You wouldn't believe how many times I tried to get rid of it with Norton, then had to rescan to find out if it was still there. It takes hours to scan that big Seagate drive. I even tried to do it in Safe Mode; still no luck. I finally realized that the file I was looking for wasn't named adware.gen. When I got the correct name, I went to the drive's Windows System32 directory. As I passed my mouse down the list, before I got to the file, a Norton screen popped up and shouted that I had a virus, and they deleted it, just like that. About an hour later, another Norton screen appeared and in a self-congratulatory manner announced to me that they had rescued me from the virus. Now, why didn't they delete it the half-dozen times I ran the virus-scan program?