Google has been saying for a while that they are interested in indexing the "hidden" web. Maybe toolbar data is used to find sites or pages without links.
As cbp said, adding a robots.txt to exclude robots should end future indexing.
Here's how you can have
pages removed from Google's index.
If it is secure information, you may want to password-protect the whole site. The easiest way is usually with .htaccess if you are using Apache. Or only allow registered users to read/post and hacking the forum so that you have to approve new members.