A coworker of mine is trying to figure this out and I haven't heard of it before. What is a "cloaked" message in Facebook?
Your coworker MAY be talking about a Firefox plugin called CloakGuard. It requires all users to have the plugin installed and allows you to obfuscate certain portions of your content on Gmail, Facebook, and a few others using a password.
Not sure how well it works and haven't personally tried it. Here's a few videos showing it in action.
I don't think it actually exists: http://www.google.com/search?hl=en&q=facebook+cloaked+message