[Perndog]

Another way this can happen is that many viruses distribute themselves by taking a name from the infected computer's address book and inserting it in the From field of outgoing virus messages, with another random name as the recipient. Therefore, if you have a friend with an infected computer, he could be sending virus e-mails with your address attached, and if he has any invalid addresses in his address book, they will send notices back to you instead of him.