Email virus

Almost everyday I get one or two sent in attachments to my Yahoo account. They are sent from different addresses everytime and I delete them as soon as they come... I've scanned my computer numerous times and use spyware and all comes up clean. All is running smoothly with the computer but why are these in my email everyday? I have a few email accounts but the Yahoo is the main one I get hit with.. I've never opened any of them after scanning them so I don't think I have any on the computer. I have spamgard turned on so they get sent to the bulk folder and not to the inbox. Anyone ever get these? I must be on a list that I shouldn't be....

Any help would be great, I'm tired of seeing these!!

I have got them a couple of times, but after a while it stops, yeah even that new spam law is not working, spamers continue to send that shit