As I understand from all I have read the person is someone you either know or who recently sent you a legit email. You might check back in your email files and look for clients etc. to see if you have ever received a legit email from him. Sircam will search a persons address book and send itself to everyone in the book. Also, it will send itself to everyone that the infected computer sends email to. Do you use eBay? Might be a buyer or seller from your eBay transactions. I suppose it is possible that you have been deliberately and personally targeted but that would be the first time I have heard of. As I said, most likely it is someone you have dealt with in the past.