There are some infections out there that can mimic you as the sender after invading someone else's address book with you in that list. However, just in case and as VirusScan isn't detecting anything try running McAfee Stinger: http://stinger.mcafee.com/
(Note that Stinger has no update feature and has to be freshly downloaded each time it is used).
Afterwards download and install Malwarebytes Free Edition here: http://www.malwarebytes.org/products/malwarebytes_free - update it before running. If an infection prevents this operation with this tool only you can do all of this in 'Safe Mode with Networking' reached by tapping F8 repeatedly while booting up and selecting it (#2) from the ensuing menu.
Run a full scan with that.
If that fails to find anything you could be OK but just in case download Hijackthis and post its log on one of the following forums:
Do not post Hijackthis logs here, we can't help you with those !
Post the logs at one of these specialist Forums:
Be sure to read all the sticky announcements/instructions at the top of each malware forum!