First, deniro apparently hasn't confirmed that the IP address in the email is actually his address.
There's nothing in that email that smells of scam...doesn't ask for info or money or anything else.
On the other hand, though, can a Mac get commandeered in the manner described?
If the IP address is spoofed (which is unlikely if the e-message is legitimate, since his ISP would have the information), the question arises as to the real IP address; checking the full headers might be illuminating.
It could be a scam if there is a hotlink to click or something similar (which deniro did not mention or rule out) which in turn would lower the window to intrusion.
That's exactly how botnets work — exactly as the e-message notes (which still doesn't legitimate the message) — and usually the commandeered computer user hasn't a clue.
