When I'm at work, I usually keep my iPod nano connected to my computer for charging and backing up the occasional file (invoices, receipts, e-mail attachments, etc.). I've just discovered that a colleague of mine has been able to mount and browse my iPod using the company network. I was, of course, horrified, as I tend to keep some sensitive documents on there (passwords for various websites, for instance). He swears he didn't open or make a copy of anything, but I've no way of knowing for sure. There's nothing I can really do about the situation, because he swears he opened it "by accident" (although he did admit he was curious to see what music I had, even though he knows full well that one cannot access the music files on an iPod in that way).
Is there a way of preventing this from happening again?