Recently I got an email with subject like "Delivery Status Notification (Failure)". It had been initially sent to my friend's old email account. The content inside that failed email was obviously one of a spam email. I wonder if some viruses infect my machine but either Kaspersky or AVG (free version) is installed in my two PCs and a notebook and it is doing fine.
My theory is that one of my friends' computers instead got some viruses and they generated such emails from a random email address to the rest of the hacked address book. Is this possible? What are your theories?
UPDATE: All the spam things have stopped since the day I posted this question. Now I wonder if my theory above is technically possible. If so, mine should not be the first and the case must be well-documented somewhere.