robots.txt and meta tags are not appropriate ways to protect confidential information. Confidential pages should be password protected.
robots.txt and meta tags are only meant to pass information to well-intended robots and search engines. Some ill-intended bots will use it to detect potential weaknesses in your web site.
If your private pages are already in Google, visit
How can I prevent my own content from being indexed or remove content from Google's index? (see the part about expedite removal).
Jean-Luc