Threats Detected after Turning Off Auto-Protect

I Updated an on-demand Scanner, Dis-connected from the Internet, Turned Off Auto-Protect, then Ran a Full Scan with the on-demand Scanner.  When the Scan Finished, I Turned On Auto-Protect again and Connected to the Internet to Check for Updates to my Norton Product; I then did other stuff on the Internet.  Then, a few hours' later, when I got the Norton 2009 Virus Definitions, I Dis-connected from the Internet and Ran a Full System Scan.  During the Scan, it found an Internet Threat.  All my other previous Full System Scans with Norton have come up Clean - except for Tracking Cookies.  This is not the first time I have did this and is not the first time this has happened, if you get what I mean, e.g. the same thing happened with a Norton 2008 Product.  I would like Users' thoughts on this please.