Yahoo email worm

Hi all,

Hopefully this is the right forum, I was curious if anyone has any experience with a Yahoo email worm. An email was still in my sent folder after I was told about a weird email from a contact, so I assume this is a worm and not a spoofing incident... also that it was still in my sent folder makes it seem like an old worm. Problem being, I have run Panda activescan/ Trend Micro Housecall/ Kapsersky's online scanner in addition to Avast! and nothing has turned up. I have changed my password and erased my address book and all non-crucial emails, does anyone have any suggestions as to another step I could take?

Thanks for any ideas!