Moved this to Malware Discussions. It's not uncommon for this to happen. It could equally as well be someone else who has your email address stored and has a similar address book and the bug is spoofing your email address in the "From" field.
As a precaution run the free version of this tool and update it before running. Let it remove everything it finds.
If you really want to have it investigated you could download Hijackthis and post its log on one of the following forums for expert guidance.
Do not post the log here, we can't help!
Post the logs at a specialist Forum:
Be sure to read all the sticky announcements/instructions at the top of each malware forum!