Virus!?!

I am a recipient of the Digest version of the mailing list.  On Monday, I was given credit for sending a message regarding aux. battery set up which I did not send.  Subsequently I have received replys from unknown persons about a message sent using my reply address with an unknown attachement.  I have Norton Anti Virus Auto Protect enabled and have detected no viruses.  I have not received any unknown attachments, so I am unsure how my e-mail address has been included.  Considering the aux. battery discussion, and the unknown attachement characteristics, it would appear that a virus has tapped into this mailing list.