ROBOTS.TXT is not hiding files

[rwhite]

NONE

[Fang]

Not all bots read the robots.txt file. Another site can have links to your files that the bots follow.
Try adding these to your documents:
<meta name="robots" content="noindex">
<meta name="robots" content="nofollow">
If you don't want your documents indexed don't put them on internet.

[rwhite]

NONE

[Fang]

Moving them to a different directory will help, but eventually they may be found again by less discerning bots.

[Robert Wellock]

Use .htaccess if you can to make the folders private or stop external sites linking via ModRewrite.

[rwhite]

NONE

[Robert Wellock]

http://www.javascriptkit.com/howto/htaccess.shtml