of course you didn't send the Virus, someone else did and it got your address from a web site or someone's address book. This can make it confusing as to who really has the virus or not. Of course the autoresponders and other people getting the virus don't know that the email headers are spoofed and send it to the address on the email.

Lucky for me, I haven't gotten any virus replies. I'm not that popular to have my email address on someone's infected Outlook machine or from a web page someone visited while infected.