Satoshi Yoshida

Will add secret message in html source in your website.

Secret Messenger

Will add secret message in html source in your website.

michaeltyson

Specify a list of tags or categories to keep hidden: These will no longer appear anywhere 
on the site, such as in the tag cloud or on the list of post tags. This is useful when using 
tags to control behaviour of your blog with other software, or when you wish to maintain 
groupings of posts out of the public eye.

Hidden Tags

Hide certain tags/categories from the public

Secret Messenger vs Hidden Tags