Update.
I ran the Malwarebytes scanner in safe mode with system restore disabled and it found nothing. Perhaps my system really is shiny and clean!
Hi,
to be sure, update your virus definitions manually, than perform a Full System Scan.
Let us know the results.
After doing as you say, the Full Scan reported no threats found. On the other hand, the computer seems inordinately slow... I'll keep watching to see if anything suspicious comes up.
You can run a scan using Norton Power Eraser. You can find the steps here:
http://us.norton.com/support/kb/web_view.jsp?wv_type=public_web&docurl=20100824120155EN
If you are not sure about any entry in the Scan Results window, please post the result here. We will help you.