Klez' trick is that if person A has it, they forge mail from B to C. So if someone you know has it, they could send mail apparently from you to other people.
You do know people who run Outlook on Windows, don't you?
Cheers, Ben
"... I couldn't see how anyone could be educated by this self-propagating system in which people pass exams, teach others to pass exams, but nobody knows anything." --Richard Feynman