I haven't looked for the hidden archive files yet (I really don't understand DOS) but I mentioned the site to a friend who knows about such things, and who didn't believe me at first: he found an enormous hidden file on his computer which took a surprisingly long time to delete.  They do exist.  Incidentally, it's not just Microsoft that silts our hard drives up with junk; I found two Netscape archive files containing email attachments (graphics files from work) that I had deleted TWICE and had thought gone; they amounted to some 70mb.