Originally posted by Minnie&Mickey
To be honest...I have no idea! I just know that it does happen, and happens quite often. At the school that I work at, I've had employees tell me that they have received emails from other employees (including myself) that had viruses attached. I even had an email a while back in my home Outlook account that said it was from me...and I'm not in the habit of sending myself viruses! LOL! Just be really careful what you open and you should be fine.
The virus infects someone's machine, and then looks in the email address book on that machine, and emails a copy of itself to everyone it finds.
What it also does is forge the "From:" address for the email that it sends. What does it use to forge the address? Why the addresses in the address book, of course. So infected machine will send email to everyone in the address book, looking as if it was sent by other people in that address book, even though it was not.
Let's use a concrete example: Peter's machine gets infected with the MyDoom virus. In his address book are entries for friends Paul, and Mary. Paul and Mary have never met, have never exchanged email, and do not know each other - they each just know Peter. The virus on Peter's machine will send email with the virus to Paul looking like it came from Mary. Paul may wonder who the heck this Mary person is and why she's sending him a virus, but she was never involved.
If you're in Mary's place, you can see that it would be frustrating to be accused of something that you had nothing to do with and have no control over.
For the record, your email address may end up in the address books of people you don't know as well. Various email programs will automatically hold on to additional email addresses that were included on email you received, or possibly from email that was forwarded. Viruses have also been known to use other sources of email addresses, or even forward them around as the virus spreads. What that means is that the simple "friend of a friend" example I used with Peter, Paul and Mary, while simple and certainly possible, is not the only way your email could show up as a forged "from" line.
What's important here is simply this: one way or another, email viruses lie about who sent them.
If someone accuses you of sending a virus-laden email, and you are positive you did not, then you have very little recourse other than trying to educate them about how viruses work. Be clear: you're not necessarily infected, nor is the person who received the mail claiming to be from you. It's some third party who is. (And identifying that third party is difficult - this is why virus writers use this technique.)
So even though people are receiving an email from you that contains the virus, you did not send the email.
See:
http://securityresponse1.symantec.com/sarc/sarc.nsf/html/w32.klez.gen@mm.html and scroll down to the paragraph intitled: "Email spoofing"
