It's possible the virus is spoofing your address, which would mean they're not coming from you, but rather someone who has your e-mail addy in their list. Run a virus check with something like Norton or McAffee to be sure.

I believe there's a hero in all of us that keeps us honest, gives us strength, makes us noble, and finally allows us to die with pride, even though sometimes we have to be steady and give up the thing we want the most. Even our dreams. -- Aunt May, Spider-Man 2