"Work At Home" Emails Spamming Contacts

I've had several people reply to emails that appear to be sent from my Yahoo Mail address, however, I've not used that address in several months (and these emails were sent in the last few days). However, when I check my "Sent" box of my Yahoo Mail and Outlook, none of these emails appear to have been sent from those locations.

All the emails give a message and link similar to this:

I'm running BitDefender real-time protection and my IE is always Sandboxed (using SandBoxie) so I don't see how this could be coming from my current home desktop.

Is this something that could be coming from another source? I've already taken the precaution of removing all the contacts from my Yahoo address book to HOPEFULLY stop it from spamming these people any further.

Any thoughts?

 

UPDATE:

Full system scans done with:

MalwareBytes
SuperAntiSpyware
Spybot
Bitdefender (Deep System Scan)

Results - Number of infected files = 0

So that rules out anything on my system.

How could this work without having infected my desktop and physically having access to my account information. IE: how could it be doing this remotely?

 

A bot huh? So how would that work? I received the spam in my Inbox, then from there it scanned my contacts and resent the emails?