I think the reason is quite simple: somebody who knows your e-mail address (i.e. anybody whom you ever sent an e-mail) got infected by the worm - and now, it's spreading to your e-mail address. I don't think you can do anything about it (there's not much use in trying to find the original infected person - because just as it's spreadying to you, it's also spreading to other people with faked "from" field - appearing as being sent from you. This way, the e-mail address spreads further).