MS Word - Email Security Bug? - Baskerville
Word files are a security nightmare because they contain all kinds of information about the editing process, which computers the file has been on, who has seen them, and (apparently) what other applications and documents were being run/open on those computers at the same time. It was Word files that exposed Alastair Campbell in the David Kelly affair.

Just to give you an idea of how much extra information is stored in a Word file, I use an office suite called OpenOffice.org, but most of the writers I deal with use Word in its many variegations. I find that when I've opened a Word file in OpenOffice.org and then saved it (back in Word format) the file is about one third smaller--one third!

Word files should never, ever be used "straight" for anything sensitive. I always use .pdf format for things like invoices and so on--generated by OpenOffice.org--butmany employers don't like that I gather because they can't edit the file easily.