One of the computers I've been using has been compromised. A message supposedly sent through my hotmail address was returned. MailerDaemon's explanation was the attachment may have had malicious code (virus, trojan, worm, whatever). I never sent the original recipient anything.
It's unlikely that the hotmail servers are infected, what with all their layers of protection. My best guess is that it's one of the public computers I've been using to access the 'Net.
I've changed passwords so that the infected computer(s) can't use my address to send people nasty stuff. If you get a message from my hotmail address-- email@example.com --with an attached word document and a corresponding subject line that runs like this: "here is the document," do all of us a favor and delete it.