in my case, and this was quite a while ago...as soon as i put the message in the preview pane, i think i just hovered over it...might have clicked it, it installed its payload, and i was screwed.
i imagine that the preview pane somehow opens the mail? since then i just watch what comes into my inbox, and delete as needed. Never open an attachment if you don't know or trust the source
I am no virus expert, but those that are, keep finding better ways to deliver them.
mark