NOD picking up viruses from Headers

Hi

I've been using Thunderbird for my emails until recently. I now have Office 2003 SP2 installed, and one of the feature I noticed is Outlook's ability to allow you to download email headers instead of the whole message from the server.

I was playing around with this feature the other day when NOD detected a virus. How did this happen?

Isn't Outlook just downloading the subject heading from my emails rather than the whole thing?

I thought NOD and all other AVs would only detect viruses when whole emails is being downloaded to your PC and not just the header...

 

Some viruses actually try to hide by including themselves in malformed headers. It sounds like NOD32 caught one of these.