Along with that you also could have some WiFi that allows folk to use and send such email.
-> Given how many machines are infected, your machine or another that used your WiFi could have sent it.
I've yet to see any successful litigation given what you've told. In fact I think it would be a fine way to shake down folk for money by threatening them.
My advice? Secure your WiFi, take Grif's advice (link will follow.)
If you can't secure your WiFi, then turn it off when you are gone.
More at http://forums.cnet.com/7726-6132_102-5098912.html?tag=posts;msg5099421
Someone recently received a spam like email from my email address with my IP or ISP address. I was the only one home at the time and did not send it from my computer. They are threatening to press charges and I dont understand how this all works. How can I prove it was not me and prevent it from happening again?