I've seen this happen before. While this case might have been a virus, it is more likely that a spammer simply used your email address as their "return" address. Then he shipped out 50,000 or so spam messages, and YOU are the one who gets the "bounced" messages. This helps them get their spam through (your email address is valid) and avoid the bounced responses (which come back to you).
This happened to a person who I help with computer issues. A pharmaceutical spammer used her email address as the "from" address on their spam messages. She had over 2000 bounced messages come back to her inbox. The spammer was one of the "Offshore Pharmacy" idiots . . . who have tons of different stupid spam URLs (pharmawarehouse.biz, pharmacasa.biz, etc.
Basically, if they only use your email address once, the undeliverables will eventually diminish and finally go away after a few days to a week or so. Its extremely annoying, but it will go away.