It seems I've had an unwelcome visitor to my Yahoo account and they decided to send out a few emails on my behalf. I'm pretty sure it was not a virus as I've been incommunicado in the bush for the past day and a half and my computers were all turned off. As it came from my Yahoo account I can only assume I had an unwelcome visitor via Yahoo. PW changed and hopefully that will be the end of it.
I'm sure someone will let me know if it keeps up.