Preventing the url from being indexed through the robots.txt is not enough. It may still be listed by search engines, unless you add the right header to you file, in the .htaccess.
Both files have to be put into the root directory of your domain.
# .htaccess
Header set X-Robots-Tag "noindex, nofollow"
# robots.txt
User-agent: *
Disallow: /
Sources: