Guru Zim sounds right on the money, I think. Check where your incoming mail is being sent from, that'll probably solve your mystery. Wouldn't hurt to have someone in your time zone fire you off a test email to check, either, if that's not inconvenient. Okies, I'll hush now. Hopefully it's nothing serious at all!
"Look. Keep your grandparents offline. I can't stand the thought of my own sweet nan coming into a chatroom to be textually spanked by someone like me."
Safe Mode. Do the scan in Safe Mode. Upgrade all definitions and then proceed to run the scans in Safe Mode. Why? Because you can (in theory) be assured that only the ESSENTIAL Windows processess and files are running/loaded.