Thanks to all for the suggestions.

So far I have run these scans, with nothing showing up; ZoneAlarm AV, DrWeb CureIT, SpyBot Search & Destroy, Malwarebytes. One thing for certain, someone, or something, has access to my yahoo list of contacts. I even received an email from myself, as predicted by kawecki.

Quote from kawecki:

If you use Yahoo web mail, your computer has nothing to do with this. Someone had his computer infected and had your email in his address book, of course he used Outlook for email. Your email is added to a list together with the addresses of the address book and other's computer address books. Then the virus begins to send email with spam or virus where the addresses of "from" and "to" are picked from the list. Some stupid virus don't check if "from" and "to" is the same address and so, you receive email from yourself.

One thing I don't understand, if it has nothing to do with my computer, how come they seem to have access to my yahoo contact list? The only thing I can think of is that they have discovered my yahoo password, and are able to log on as me.

@rokket

Quote - And amazingly enough, I am still seeing the email from Nigerians who have 30 million in cash they want to give me if I just give them my bank account numbers...

The Nigerians are trying to cheat you, hold out for 50 million. ;)