AVAST is another free, but effective antivirus. I have used it for a couple of years now and it does a bang up job, and is updated sometimes twice a day. It has great detection, and in the last two+ years has given me no false hits.
As noted above, scans can take a long time. Hang with it though as if this is a virus in your boot sector, once it finishes its scan, the program will need you to reboot so it can scan your start up files. Then it will finish up.
No antivirus/spyware is 100%, and some pick up things others won't. Don't be afraid of the free stuff (remember though, they *love* an donation or actual purchase!) as it turns out most of the free stuff like AVAST, AVG, and Trend Micro test nearly as good or better than Norton and McAfee.
They also take less resources from your machine, and if you delete them, they are gone. Just try and get rid of Norton..... I have had it on twice on two different machines, and it can't even uninstall itself. There are bomb fragments all over the machine when you uninstall, and if you don't run a registry cleaner it will still loads remnants (or at least try to) of the program.
McAfee..... two commercial versions later, and too many false positives to count. Both programs are bloated larger than the Hindenburg, and while they test out well in most cases, you will find the tests are run on newer machines with a lot of available resources. If your machine is older, say more than a couple of years, those two programs will slow your machine considerably.
Good luck, Zz. It sounds like this is an easy fix.
Robert