I just noticed a file in the root of a Joomla site called google574329fsa8e78.html (numbers are not exact, but close). Normally I don't pay attention to it (thinking back to the time I used to verify Google Apps using html file upload), but with this site in particular, I saw that the file was huge - 750K. I opened it and then saw that's it's a textual representation of a TON of static content on the site. Content which should be only visible to registered users.
Any clue how it got there, or what it's purpose is?