Windows Defender showed MyDoom on my system. Clicking "Remove" showed "Fail". NAV (part of SystemWorks 2004) didn't catch MyDoom. I ran the MS Malicious Software Removal Tool (Feb 2006 version). This said "No Infection". Defender then gave the all clear. Why didn't NAV pick this up? Is it this a false negative from Defender?

Checking the NAV Status Page shows: OK (all green ticks). But when I go to "Options\NAV\Other\Threat Categories\Virus Threats" the top box (Viruses, worms, trojans (scanned by default) and its tick are greyed out and can't be changed. Is this a problem?