Intrusion alert!

[tinyjo]

OK, it's much worse than I thought. Someone else is sending out a ton of spam email purporting to come from my domain. It seems to be the style of spam that I've been getting recently (prescription meds stuff) so I assume that's where they found the domain name. Now the question is, how do I get them to fuck the hell off and stop doing it? I figured out that it's not being sent from my computer because after disinfecting it, I shut it down for a bit as a test and logged onto my email using webmail and my office computer. And I've just received another bounce message stating the original mail was received at 9:06 EST (i.e. 14:06 GMT). While my laptop was turned off, and had been for a good hour. On the plus side this means that I can turn the laptop back on, reassured that it's completely clean of mail sending crap but on the minus side, what the hell do I do about this?