I'm sorry to disagree, however i am certain it came from ecomodder.
the only other sites i had open at the time were Hotmail and Craig's List.
the status bar on ecomodder said "waiting for xpscanneronline.com....."
Ecomodder 1/2 loaded and did not complete loading until i canceled the popup.
it was a script msgbox type popup and not a new window browser popup.
I'll double check my history to be sure, though. i hate making false alarms.