Google Notebook users are apparently making personal information, such as Social Security numbers and e-mail passwords, available through the online bookmark service.

Links to the sensitive information were posted in a comments section of Digg.com, a news site in which users contribute and vote on stories found on the Web. The popularity of items determines their placement on the site.

The personal data was found using Google's Notebook search, an experimental service available through Google Labs. Notebook, launched in May, enables people to bookmark whole or portions of Web pages, and to organize the content in folders. The bookmarks are either done through a "note this" link on Google search results, or through extensions for Internet Explorer or Firefox Web browsers.

Bookmarked content can be made public or kept private, but it appears some users have failed to make good use of the latter. Google was not immediately available for comment.