It went on for several days, and I received a bunch of teasing emails from friends - and a couple of "Please take me off your mailing list ......." I tried a couple of things before I finally got this explanation and advice from Norton, my virus and spyware guys :
The spammers usually don't get into your computer (check - I did every scan known to God and man and found nothing ). Rather, they actually hack the internet service provider that manages your email account. The simple yet elegant solution is to change the password on your email account immediately if this problem arises. My Norton guy suggested changing your email password monthly, for safety's sake.
So there's your internet safety tip of the day - pass it on, so no one you know will ever have to become a Viagra salesperson !